omae2012-84124- als unconventional

1 Copyright 2012 by ASME

Proceedings of the ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering OMAE2012

July 1-6, 2012, Rio de Janeiro, Brazil

OMAE2012-84124

ARTIFICIAL LIFT MANAGEMENT: RECOMMENDATIONS FOR UNCONVENTIONAL OILFIELDS

Clemente Marcelo Hirschfeldt OilProduction O&G Consulting Comodoro Rivadavia, Chubut,

Argentina

Fernando Flores Avila PEMEX E&P

Poza Rica, Veracruz, Mxico

Jaime Granados Cliz PEMEX E&P

Poza Rica, Veracruz, Mxico

ABSTRACT

This paper presents concepts and recommendations regarding Artificial Lift Systems (ALSs) management during productive life of oil fields, envisioning: selection, acquisition, installation, monitoring and evaluation criteria, as well as subsequent inspection thereof, and highlighting the more important that applies particularly to unconventional oil fields. Issues analyzed herein involve definitions of roles, functions and competencies related to operator as well as service companies and sectors involved or required to live up to the challenges posed by these systems. Two scenarios that represent Latin American region real cases are presented and illustrated with the analysis of these ALSs management topics; one of them, the oldest productive basin in Argentina, as an example of conventional oilfields with experience in Artificial Lift Management and the other, an unconventional field recently re-activated with an accelerated development pace, being exploited in Mexico. Conclusions are presented in terms of that ALSs Integral management should be taken with strategic and integrated vision, in accordance with current level of development, future plans, and complexity of the field; not only focused on maximum oil production, but also on optimizing production costs; and contemplate all parts commitment that add value to the whole process.

1- INTRODUCTION

Whether from the beginning of the exploitation of the reservoir it does not have enough energy, or it is a mature field, when energy is insufficient to promote natural flow from bottom hole to surface facilities, or occasionally to obtain more production; it is claimed that more than 90% of the oil producing wells worldwide require ALS in order to solve this

challenges and make their exploitation economic and technically feasible. In many conventional fields around the world, ALSs play an important role in oil field production process. Selection, acquisition, installation, monitoring, evaluation and subsequent inspection of these systems, involves different stakeholders, including internal and external sectors or companies. Besides, if factors such as field location, local culture and involved parts experience are added, understand and analyze all of them is important, not only to maximize an specific ALS run-life, but also to maximize and optimize field production and costs in an effective manner. Another important factors are the stage and dynamic of the fields development, whether is new or old, or those subjected to EOR technologies, such as secondary recovery by water injection, where field requirements and conditions change on a continuous basis. On the other hand, development of certain unconventional oil fields, presents particular technical and management challenges, among them, those because of the massive use of ALSs. In many cases technologies and methodologies applied to conventional fields could be applied to unconventional fields, but requiring more rigorous analysis of some factors, such as ALS mechanical limits, for example, and also increase and improve management and performance monitoring models. Analysis under this management model uses several concepts that make it integral and suitable for unconventional reservoirs.


2 GOLFO SAN JORGE BASIN, ARGENTINA The Golfo San Jorge Basin (GSJB), located in the central Patagonia, is the oldest productive basin of Argentina, where the first economic discovery took place in 1907, in Comodoro Rivadavia (Figure 1, Annex A). GSJB is the oldest and most prolific Argentinian productive basin, producing 279,302 bpd of oil, and 2.950 MM bpd of water, with 13,831 active oil wells (December 2011). Due to the mature state of the basin, every year, new waterflooding projects are implemented, but in deeper reservoirs resulting greater gross production per well, every new project. The Main characteristics of this basin are:

Faults and sand stone lenses HWOR (high water-oil ratio) Increasing fluid flow rate per well Complex fluids: corrosive, heavy oil, gas, sand and scale Multiphase flow Multilayer reservoir: from 1,800 to 9000 feet Vertical wells (5 casing) Semi-desert environment

Within this context, selection, operation, optimization and management itself of the different ALSs play one of the most important roles during basin development. 2.1-Artificial Lift Systems experience From the beginning of oil industry in Golfo San Jorge Basin, several ALSs have been used to produce oil the wells. At the present time, systems as Sucker Rod Pumping (SRP), Progressing Cavity Pump (PCP) and Electric Submersible Pump (ESP) are the most popular systems used to produce 98 % of the total basin fluids, and smaller quantities of hydraulic jet pump (HJP), plunger and gas lift systems (GL) are used. ALSs are distributed as follows: 10,253 SRP; 2,035 PCP and 1,474 ESP. Close than 90% pumps are installed between 3,000 ft and 8,000 ft depth, producing flow rates over 1,500 bpd. Deeper target reservoirs and wells with higher flow rates mean a permanent challenge for the different ALSs and specialist involved. 3 - CHICONTEPEC BASIN, MEXICO Tertiary Gulf Oil (Aceite Terciario del Golfo) or Chicontepec Proyect (PATG), with an original volume in situ surrounding 100 billion boe, has the objective of contributing in a substantial measure to PEMEX Strategic Program goals, speeding up recovery reserves not only by quick incorporation of new productive fields, drilling an important number of wells per year, but supporting production platform giving special attention to maintain and increase base production by keeping wells operating efficiently and restoring shut down wells. However, its development requires unprecedented capabilities in the oil industry, with important challenges like:

substantial investment, substantial increase in execution capacity, use of new and selected technologies, best practices in all the exploration and production processes to increase oil recovery factor and profitability of the project, and others; all of them are being confronted.

PATG is located at the Gulf of Mexico Coast Plain (Figure. 2 Annex A) and currently covers near 4,300 km2. It was discovered in 1926 and began to produce in 1952 but marginally to 1970, discreetly developed from 1971 to 1991, and strongly reactivated particularly at the end of the past and beginning of the present decades. Currently (feb-12) it has 2127 producing wells and 582 shut down wells (with possibilities). It produces around 65,000 bpd of 18-45 API oil and more than 130 MMcfd (Oct-11). The project has near 40% of national 3P reserves and itself performs a large volume of work (Figure. 3, Annex A). In order to better control, PATG is divided in 29 Fields and classified in eight Sectors as shown in (Figure. 4, Annex A)

3.1- Geological characterization PATG, the biggest basin in Mexico, covers Chicontepec Paleo-chanel geological limits, is a tertiary sub-basin developed into the Tampico-Misantla Basin. Reservoirs are constituted by thin alternated sand and shale rock layers of inferior Eocene superior Paleocene ages, showing up to 1,000 m. gross and 1- 15 m. net thickness, 8-12 % porosity, 0.1-15 md permeability and 50-330 kg/cm2 initial pressure, as main characteristics. 3.2-PATG, understood as unconventional reservoir Fractured, tight and unconventional petroleum reservoirs, although less common and less well understood than conventional sandstone and carbonate reservoirs, have become an increasingly important resource base. Usually, oil and gas shale, tight-gas, heavy oil reservoirs, and coal beds are the main sources of what is known as unconventional hydrocarbon resources; also unconventional resources typically are oil and natural gas resources that exist in geographically extensive accumulations and when the assessment methodology and production practices vary from conventional resources. Geologists and petroleum engineers find that traditional technics for conventional reservoirs are often insufficient or ineffective for unconventional reservoirs, which interpretation involves emerging exploration strategies for a better understanding, and new drilling-completion and production technologies in order to optimize productivity; opportunely new and emerging approaches and technologies are being used to delineate and develop them. Since 2002, a new development of PATG began, and with knowledge acquired until nowadays, important technical challenges have been recognized; among the principals are:


Highly stratified, heterogeneous, discontinuous, and low permeability reservoirs; demanding arduous reservoir characterization studies and strategic wells to define the more productive zones.

Conventional wells with strong and fast production declination; demanding unconventional wells on the base of specialized productive studies.

Low recovery factors, due to the initial pressure just above the bubble point pressure causing short flowing well periods, in the most of the cases. Consequently ALSs are systematically required to support base production. Additionally, secondary or enhanced oil recovery systems should be evaluated.

Because of extension, topography, and highly quantity of wells needed to the exploitation, facilities optimization is mandatory.

Within the framework exposed, as a huge Project in terms of extension, reserves and scopes, complex in reservoir characteristics, particularly because of its low permeability and pressure, with marginal oil production wells dependent of massive stimulation and ALSs use, or special recovery systems; and challenges like already exposed that requires specific technologies and management models; and according to the Oil Resources Triangle Classification (Figure.1), PATG is being understood as an unconventional case.

Figure 1 - Oil Resources Triangle Classification

3.3 Artificial Lift Systems in PATG To exploit fields of the different projects of PEP (Pemex Exploration and Production), several technological challenges are confronted, among them, those related to wells productivity, particularly because they do not have enough energy to flow by themselves from bottom hole to surface facilities. Most of the flowing wells in the assets of the North Region of PEP, where PATG is located, early present this problem, which mean that ALSs take significant role and

widely application. In this region, diversity of well conditions has promoted to test a variety of ALSs, and to establish several of them as common use, where ALS selection has been primarily based on: observance on better worldwide practices, suppliers influence, own experiences and technical-operative staff preferences. Actually, SRP predominate (60%), followed by GL which was the first one of massive use (33%), PCP (5%) and HJP (2%), recently subjected to field tests trying to expand their use. In PATG case particularly, statistic is similar: SRP predominate (70%), followed by GL (25%), PCP (4%) and HJP (1%), 3.4- Artificial Lift Systems Challenges The use of different ALSs in PATG involves not only technical challenges, but also since management point of view. The most important technical considerations for ALS selection are: because of the reservoirs characteristics, wells production decline hard and quickly, demanding artificial lift system early in their productive life; diversity of reservoir, fluids and wells characteristics make difficult to identify where, when and which one of the different systems better apply; and well geometry (dog severity and azimuth), which means special attention on design. Since the management point of view, the principal topics to consider are: extension of the project, several work areas involved, vertiginous development and few experienced personnel demand to analyze and to improve artificial lift management schemes in topics like selection, design, operation, maintenance, optimization, procurement, contracting and integral management itself. Identify and learn appropriate technology, just as operational and administrative best practices, are considered key elements to support a better ALSs integral management. Based on reservoir characteristics and PATG development plan (number of wells and complexity), ALSs application presents several challenges, some of the main are listed below:

Low permeability reservoir (0.1 5 md). Low productivity per well (average around 35 bpd) Biphasic flow at the reservoir. Noticeable and early reservoir energy level drop (first

three months). High back-pressure at surface. Dog leg severity up to 7 /30m (Figure 2) Well deviation (type S). (Figure 3) Sand production from hydraulic fracture

completion(always needed) High Gas-Oil Relationship (GOR) > 200 m3/m3 Several participants involved Accelerated development Lacking experienced personnel


Figure 2 - Dog Leg Severity examples

Figure 3 Well deviation type S

4 ALS MANAGEMENT CONCEPTS The comprehensive management cycle of Oil field development using ALSs, involves different inherent processes and participants, which makes necessary an integral scheme of management. Identifying each of the stages and people who take part in the processes is fundamental to be able to optimize existing procedures or implement a compre-hensive medium and long-term management strategy. The scheme in Figure 4 illustrates a management cycle during ALSs implementation and operation, and can serve as a guide to analyze different aspects of the whole process. Two stages

are identified: initial evaluation, for initial selection and implementation; and the Integral Management ALS Cycle, which by its own development, it becomes in a positive feedback cycle (virtuous circle) where different work participation areas and interdisciplinary work becomes key factors for a correct management.

Figure 4 ALS Management Cycle This cycle starts with one or more ALSs alternatives selection based on the analysis of information on the reservoirs to be produced, well construction data, and other aspects that will be discussed throughout this paper. Based on this analysis and once the best method(s) have been selected, equipment acquisition, installation and operation are the next stages, which complete and closes one of the first sub-cycles in a comprehensive management system. Once wells have been started up, monitoring and control operating variables are essential not only to guarantee optimum ALS operation within established parameters, but also to maximize reservoir production. Continuous analysis may point out the need to work on the system in operation, either based on surface actions like (changes in sub-systems or some operating condition), as well as down-hole actions;, either by replacing elements, or the whole installation, or even the type of ALS in certain area, in order to meet development objectives. Components failure on already installed and operating ALSs is another situation that may happen, which corresponding analysis and evaluation thereof, should provide information for decision making in future ALS selection and/or design. In other cases, when ALS mechanical limit has been exceeded, oil field development strategy may have to be redefined considering topics like implementation of secondary recovery projects, rethink of geometry and well depth, etc.


The management cycle above explained, represents in summary the know-how in artificial lift management in Golfo San Jorge Basin (Argentina), where widespread use of ALSs since the beginning of its operation is common. However, this work strategy could be considered for other kind of oil field operations.

4.1- ALS Management Model Different ALSs management models will depend on the experience of the operating and services companies and of their professionals. A company (field operator) with wide experience on the use of ALSs should be in condition to: evaluate and select products, services and companies associated offered on the market, processes that should be leaded by production engineering sector and supported by operation sector and service companies. Depending on the scope of these companies, many times acquisition takes place by alliances (between operators and product/service suppliers companies), which usually include issues like maintenance, inspection, monitoring and engineering services, among others. Production engineers of the operating companies also should play an active role in equipment testing, performance evaluation and failures analysis, at either their own facilities or laboratories or those of the service companies. This model is usually based on the knowledge of operator needs, supported by the experience of a specific company; it could be represented in the figure below:

Figure 5 ALS Management Model

This model is usually based on the knowledge of operator needs, supported by the experience of a specific service company.

4.2- ALS Selection and Design ALSs selection criteria have been analyzed for the last 40 years in the industry however it is important to review some of the most significant criteria and considerations on this topic. Selection criteria include but are not limited to the following:

Theoretical-practical knowledge (advantages / disadvantages; mechanical limits, technical advances, knowledge of the particular case, etc.).

Selection through expert programs. Selection by comparison of Net Present Value (NPV).

Based on the experience of companies using different ALSs, the conjunction of these ALSs selection methodologies is common practice, so more than one is usually used. Selection and design are processes intimately linked, and they should include a vision of the present as well as the future field development, without disregarding past experiences. Also, they include multidisciplinary participation, mainly in fields subjected to continuous and/or changing development strategy. These processes definitely begin with the drilling and termination planning, just as with the awareness of the development strategy and the related implications for the involved wells, which productive life could eventually consider more than one type of ALS. When a well is designed (diameter and route), many aspects should be shared in advance with those participants who will play a direct role in ALS selection and design, because multidisciplinary analysis could limit the type of systems that can be used or maximum production capacity thereof, and therefore affect the development of the reservoir. In addition, reservoir department should provide information on the production forecast based on any development plan present, considering secondary recovery implementation if the project entails the case. Knowledge of the particular case (rock, fluid, wells potential, wells geometry, surface installations, power supply, space, environment, security, statistics, and maintenance cost operation) by all those implied is important, and essential input information for selection and design processes. Mechanical Limit as ALS Selection and Design Criteria, can be analyzed from different approaches. The capacity of the system to transfer power from the power unit to the pump is one of the most important factors to be considered on the analysis. Hence, casing diameter becomes one of the most important border conditions because not only tubing diameter is restricted, but also other elements such as sucker rods, valves, valve mandrel, or centrifugal pump shafts, depending on ALS type. In general casing and tubing diameter reductions, restrict ALS equipment and tools dimensions, and as consequence, restrict flow rates, gas handing, and maneuverability during well interventions and information capture. Other border condition is the depth, particularly


because of the limits to resistance, pressure and temperature, directly dependent of this parameter, of different elements of the hole system, particularly in down hole. Another critical factor on mechanical limit criteria for maximizing ALS systems reliability is premature materials wear. An everyday task for Production Engineering Departments is to deal with unpredictable failure occurrence of the different ALS elements that exceed that mechanical limit. Failure analysis and subsurface equipment testing following equipment extraction are fundamental when it comes to make decisions regarding ALS repairs, or new designs or selection. In addition, if the corresponding root-cause analysis concludes that ALS mechanical limit has been reached, a change of ALS type or exploitation strategy could be required. 4.3- ALS performance evaluation and optimization ALSs analysis requires appropriate and quality logging of operating variables, which is fundamental in order to make right decisions. Regardless whether variables are taken manually or automatically (sensors/recorders), their integration and examination is important in order to better support decision-making in performance and optimization analysis. Main variables to monitoring include: production measurement, surface and downhole pressure and temperature, fluid levels (dynamic pressures), and operating parameters depending on ALS type like: torque and electric current, loads in surface units, loads in rods; pumping speed in revolutions per minute or strokes per minute -PCP and SRP-; downhole vibrations, downhole equipment temperature -ESP-; gas injection and discharges frequency, open and close valve pressures GL-; injection and production flows, pressure and temperatures HP-; for mention some of them. Again, like in selection and design processes, in optimization process practical-theoretical knowledge is vital. And in this case is particularly important to recognize productive potential (maximal reservoir potential of total fluids) and operative potential (maximal well/system oil production potential), considering optimal ALS operation, without exceeding mechanical limits of its different components), which determination will permit to establish appropriately optimization limits and goals. For this proposes, at least three sectors are considered key sectors (Figure 6):

Reservoir department, related with productive potential, production forecasts and general information necessary for well and ALS designing;

Productivity engineering sector, linked with operative potential, and based mainly on the productive potential and mechanical limits, carries out optimization, but taking care of aspects like water channeling, formation sand and excess free gas production, as well as development strategies, among others;

Production Operations, directly involves in to achieve operative potential, based in applying by direct actions the operative conditions according to design settings and taking care of known limits, also is important the permanent collection of information and monitoring of the performance system.

Figure 6 interaction between key areas

The most and better information related should be interchanged among these main sectors and also should be the source of periodical meetings to identify requirements, opportunities and support necessary actions and programming itself focused on permanent ALS optimization.

4.4-Inspection and failure analysis As regards ALSs management, logging, analysis and statistical monitoring failure are important when it comes to providing feedback for the decision-making circuit. It is well-known for example, that a recurring failure in a ALS sub-superficial key element, not only causes production losses, but also involves associated costs by pulling services used to replace elements of the installed system; also for example superficial aspects like type of location/environment where the system is installed (jungle, sea, remote fields, etc.), not only mean an hazardous environment for the surface elements, but also higher associated costs, and at times, impossible access with appropriate equipment to intervention in time and form. When an ALS is being used, after retiring surface or subsurface elements previously used, different inspections should be part of the work routines. These processes not only give the chance to evaluate the performance of the equipment removed, but also enable more in-depth failure analysis, for example root-cause analysis. In order to decrease wells shut off by superficial or sub-superficial failure causes, is necessary to investigate causes of incidence and also to consider the optimization of the whole ALSs, element by element. Even that reuse of materials does not mean that low quality elements are going to be reinstalled, if certain criteria are met, the reuse of sub-surface components can be considered,


because is necessary to bear in mind that one of the global objectives is to maximize the life cycle of production wells. In addition, proper classification of materials based on the traceability of their history will help to reduce production costs. Dependable data bases are very useful, in order to be able to identify type, mode, cause-root of failures, as well as to determine reliability and availability indexes, and to optimize ALSs operative parameters in a continuous manner. When production costs increase significantly, in many fields, inspection and the reuse of subsurface elements is fundamental in order to maintain the profitability, but in order to do so, the operating company and the professionals in charge have to become directly involved in the process. 5 ALS INTEGRAL MANAGEMENT IN UNCONVENTIONAL FIELDS Based on experience in ALSs management for conventional fields such as showed for GSJB in the above section, as well as on findings of a recently completed ALSs analysis for the PATG; concepts and recommendations that could be used for unconventional fields, will be highlighted in this section:

Formal work schemes that clearly identify participants, roles, functions, responsibilities, inputs and products for all involved areas, will permit to benefit aspects so important like: information interchange, coordination of activities, teamwork and common: goals, objectives and achievements. Actors and activities identification for each process and stage is essential to establish and to optimize relevant procedures and implement integral management strategy to medium and long term. To define these schemes is very essential for unconventional fields where high quantities of wells are involved and more if the development pace is accelerated.

Periodical production meetings (well by well review),

where relevant aspects, particularly between Productivity and Well Operation responsible areas are reviewed, have as main objectives to identify, to prioritize and to allocate resources to complete activities focused to get production increases, a typical key target. The interdisciplinary interaction and information interchange in order to take the better decisions well by well also becomes a key action where high quantities of wells are involved.

The positive feedback cycle by training and continuous

improvement and as result of its own progress, it becomes itself in a virtuous circle, working towards its own optimization. This concept could be considered universal, but essential to optimize production and costs in this kind of fields.

5.1 ALSs selection criteria based on experience Two stages are identified during ALS implementation and operation; initial evaluation and the Integral Management ALS Cycle, which are represented in the figure below these two main stages of this process, based on experience in the management of ALS are presented at the (Figure 7)

Figure 7 - ALSs selection criteria based on experience

During the first stage of ALS implementation, usually there is not historical information related to performance indicators, so that continuous monitoring of operating variables, failure indicators and the knowledge of others experiences (benchmarking) are part of this phase on which a primary selection of the best alternatives for ALS is based, and continues with an ongoing assessment to reach the most appropriate ALS for the case. 5.2 - Selection criteria based on mechanical limits

During the second stage of the hole process, design, operation and optimization sub-processes come into active play, several challenges are faced, many of them particularly present and or exacerbated in the case of unconventional fields. Complexity of many of the non-conventional oil deposits is not only present in terms of the characteristics petro physical of the reservoir and of the fluids contained, but also in the geometry (dogleg severity and azimuth) and completion characteristics (fracture hydraulic or other stimulation technics) of producing wells, which make these reservoirs and wells unconventional themselves. Some factors related to ALS mechanical limits for unconventional reservoirs, that should be considered are:


Dog leg severity and azimuth Mainly in ALSs using sucker rods (SRP and PCP), system reliability is based on minimizing wear between tubings and sucker rods, as well as sucker rods fatigue. In both cases the use of anti-wear mechanisms is essential. For ESP applications, Dog leg severity could affect to power cable integrity as well as to engine and seals. ALSs Systems without sucker rods like HJP and GL could be evaluated as alternatives, their use should be analyzed depending on the expected time between failures. Gas handling Depending on natural and/or mechanical gas separation that can be done, this condition may limit the use or the volumetric efficiency of systems such as SRP and PCP. In the case of reciprocating pumping it may cause partial filling of the pump resulting since low efficiency to total lock (gas lock). On the other hand, with PCP systems, even when certain amount of gas is controllable (without locking), too much gas may cause poor lubrication between stator and rotor, and subsequent rupture, gas absorption by the elastomer or an heterogeneous pressure distribution along the pump stages can create pump failures or poor performance of the system. For ESP systems, gas separators, Advanced Gas Handler (AGH) and/or multiphasic pumps will be required, depending on the gas-oil relationship (GOR). Systems as gas lift and plunger lift (depending on the flowrate) are friendly to the handle and use of gas. Compatibility with fluids produced Mainly associated with PCP systems, where compatibility of the elastomer of the stator with fluids produced is essential to ensure the life of the system it. So, is imperative to predetermine presence of Aromatics, H2S, CO2, among other components, as well as implement elastomer compatibility testing with wellbore fluids before installing. If the fluid composition produced is unknown, less susceptible systems should be considered for the evaluation of wells.

Flexibility in flow rate produced Whether during an abrupt production decline phase, such as in the case of low productivity compact deposits, or for increasing production areas under EOR processes, ALS systems flexibility to accommodate wide well production rates, without major modifications to the surface or subsurface installation, is essential. Uncertainty in the productive potential Uncertainty in the productive potential, coupled with a sharp production decline may result in an operational condition called "Pump-Off", in which no more fluids from the reservoir enters to the pump. To prevent this condition, the operation with increasing flow rate and a strict fluid level monitoring should be realized. In the case of PCP systems, this condition is critical because the stator elastomer requires to be

lubricated, and the use of downhole pressure and temperature and variable speed drive (VSD) sensor should be considered. In the case of ESP systems, if it shall be subject to very low fluid velocity to cool the engine and also by the lack of fluid, these situations will cause motor failure or stop of low current to the motor. Under these conditions, downhole pressure and temperature monitoring systems and variable speed drives (VSD), are valid alternatives to protect the equipment. If the productive potential is unknown, high capacity and more flexible systems should be considered for the evaluation of wells.

Well depth Fluids production from wells is directly related to hydraulic horsepower concept (the higher pressure and flow to be pumped, the greater horsepower required). Systems that use sucker rods as PCP and SRP, will be limited to maximum mechanical capacity of the sucker rods. GL and HJP will be limited due to the injection pressure available of gas and water respectively. For the ESP systems power transmission is limited by the capacity of the motor drive, seals and pumps shafts. Down-hole temperature The two most vulnerable systems to downhole temperature are PCP and ESP. In the case of PCP, temperature can affect elastomer swelling rate, as well as cause degradation of its mechanical properties. The temperature of the elastomer during the operation will depend on the downhole temperature, fluid refrigeration capacity and the heat-build up of the elastomer (hysteresis). In ESP systems, the temperature affects mainly dielectric properties of the motor and cable, as well as lubricating oil properties thereof. Equipment selection validating temperature resistance of materials and compatibility testing are recommended. Solids handling Sand production during first production stage of hydraulic fractured wells is typical. Internal components Stuck as well as subsuperficial pumps completely plugged are usual. At this stage PCP or HJP are often good alternatives which performance combines well with sand production until it is stable and not displaced from the completion. Slim Hole Wells Slim-hole wells have different restrictions for its completion. Casing inside diameter (ID) determines outside (OD) diameter of the tubing string, and this limits OD of the sucker rods and other internal components. A slim-hole well could restrict the OD of the ESP components as motor, seals and pumps, and its limit the diameter of the shafts. In summary, the power transmission from the motor to the pump is limited when PCP, SRP and ESP are used in slim hole completions. If a tubing-less completion is used, other mechanical challenges will appear in order to install and operate any ALS. Particularly in


slim-hole wells, diverse operations in completion, intervention, wireline, and ALS operation themselves, become more difficult, increasing time, risks and costs. 5.3 Optimization process based on knowledge and plural participation. As it was pointed out in section four, in optimization process the ALSs practical-theoretical knowledge is vital, and to complement the analysis is important to implicate the understanding of the particular case in associated factors (rock, fluids, wells potential, surface installations, energy supply, space, environment, security, statistics and operating and maintenance costs, productive life; strategic development plans etc.), that eventually can suggest to consider more than a type of ALS.

The learning curve and the virtuous circle concept take particular importance in relation to the optimization process. Based on technical and economic information (mechanical limit analysis, statistics of performance, failures and maintenance, as well as of associated costs) during learning curve and in a cyclic manner, it is required to establish data bases and information feedback among overall involved areas, in order to support interdisciplinary decision making in selecting, designing and/or optimizing ALSs.

Another essentials aspect to maximize evaluation and optimization processes effectiveness, particularly important for unconventional cases and strongly linked to ALSs integral management are: work methodology establishment, defining common and individual objectives, roles, responsibilities, and deliverables, particularly among main involved areas in the process as are Reservoirs, Productivity and Operations department. Periodic work meetings, called production meeting or well by well review, where in an interdisciplinary manner interest cases are reviewed and actions pointed to wells optimization, and the responsible areas are agreed; performance indicators and failure statistics setting up, as support to do the analysis of operating evaluations and diverse problematic trends, root cause analysis and to define possible actions; a whole vision of the processes involved within ALSs integral management, which means integral and specialized training.

Incorporating KPI`s on inspection and failure analysis. When it comes to make decisions during the whole production process, as a complement to optimal ALS selection and design process, and as basic part of the ALS optimization process, monitoring of ALS operations and ALS failure rates are essential for the evaluation of ALS performance and the run-life of each system thereof, as well as the associated costs. These tasks can be supported in the use of Key Performance Indicators (KPI), as statistical tools; classic indicators include:

API (Annual Pulling Index) This indicator usually logged month by month allows the visualization of the number of failures by wells and making forecasting based on average in one year. It is expressed in #Interventions/well/year. For example, for a population of 100 production wells and, a monthly average of five interventions with pulling equipment due to failures in the wells, we have: API= (N of interventions)/(Running Productive wells) 12 months=5/10012=0,6interventions/well/year This means that each well would fail 0,6 times per year, or that the life cycle of a well is approximately 1,6 years. This simple indicator can be applied to monitor failures per well, per field, per ALS type, per system element (rods, pump, tubing) 5.4 Recommendations for ALS implementation in unconventional and new fields As a summary of this paper, some recommendations are presented which could be considered for the implementation of ALSs in unconventional and/or new fields: Theoretical-practical knowledge about ALSs (principals,

advantages/disadvantages; mechanical limits, technical advance, etc.).

Particularly case knowledge (rock, fluids, potential wells, surface installations, energy supply, space, environment, security, statistics and operating and maintenance costs, etc.)

Depending on the stage of the productive life of the field and the strategic development plans, different types of ALSs eventually can be considered during the productive well life.

Economic (investment, operation, maintenance). Learning curve/ virtuous circle:

o Based on Technical and Economic information (mechanical limit analysis, performance statistics and failures, as well as associated costs) during learning curve and in cyclic form, it is required to establish data bases that make possible analysis that support ALS selection and/or optimization decision-making.

o Once ALS operation starts, information feedback from overall involved areas (historical events registers, (failure, operative problems, corrective actions, etc.) comes essential for re-design/optimization.

The ALSs selection process start with the drilling and

completion design Implement actions to improve quality, quantity and

opportunity to obtain information for SAEs design and re-


design, particularly measurement and fluids characterization, pressure information, temperature, dynamic level, etc.

Improve sub-surface equipment availability that helps to achieve design specifications.

Well schematic related to completions, conversions, and workovers to ALS must be information deliverable from Productivity Engineering and should be delivered among overall involved areas: intervention, operation, maintenance, reservoirs, etc.).

Warning in particular conditions changes. Some ALS are vulnerable to reservoir dynamic conditions changes, but it does not mean that the system cannot operate or should remain once certain conditions are stabilized.

Consider that determining Inflow Performance Relationships curves (IPR) by using methods that take into consideration production real test and dynamic and static pressure, derived from logging and/or pressure gradients and fluid levels by echometers.

Define exploitation optimal point (PWF vs Flowrate) and the optimal potential.

CONCLUSIONS Although strategies to develop oil fields may be strongly influenced by the maturity of the fields or by the corporate philosophy regarding field development itself, ALSs management should be taken on with a strategic, integrated vision in accordance with the future development plans for the field. ALSs implementation criteria presented in this paper are considered pertinent on developing any oil field, but needed for unconventional fields, which require greater commitment mainly due to potential complexities related with drilling and completion of wells, as well as with the uncertainty in the productive potential or with the abrupt production declination, among others. In these cases it is very important to know the mechanical limits of the available ALS, to select the more confined in a first step. In the other hand an increasing number of production wells with ALS in a field, will require the implementation of management schemes or work methodologies involving analysis, selection, design, operation, optimization, etc., not only focused on maximum oil production targets, but also on taking care of the important economic impact that products and services associated with the ALSs have on production costs. All processes involved not only requires a firm commitment by the different sectors involved in field operating companies, but also by the companies that provide products and services, from which quality products and services, and experienced personnel is required, as service companies that adds value to ALSs integral management. Also is pertinent to consider sufficient and adequate scenarios and avoid rigorous

contractual schemes that limit technical initiatives or do not meet the necessities of the case.

The already mentioned virtuous learning circle for the whole ALS management scheme should be a key objective, in order to get the optimal integral management results.

NOMENCLATURE AGH =Advanced Gas Handler ALS= Artificial Lift Systems API =American Petroleum Institute or (Annual Pulling Index) bpd.= Barrels per day CO2 = Carbon dioxide EOR= Enhanced Oil Recovery ESP=Electrical Submersible Pumping Ft=Feet GL=Gas Lift Pumping GOR=Gas Oil Relation H2S=Hydrogen sulfide HGOR=High Gas-Oil Relation HJ=Hydraulic Jet Pumping HWOR=High Water-oil Rate ID=Inside Diameter IPR=Inflow Performance Relationship kg/cm2. - kilogram per square centimeter Km2=Square Kilometer KPI=Key Perfomance Indicators m=Meter m3/m3 = cubic meter per cubic meter md=millidarcy MM bpd.= Millions of barrels per day MMcfd=Millions of cubic feet per day (of gas). NPV=Net Present Value OD=Outside Diameter PATG.- Aceite Terciario del Golfo or Chicontepec Proyect PCP.- Progressing Cavity Pumping PEP.- PEMEX Exploration and Production PWF.-Downhole Pressure Well Flowing SRP.- Sucker Rod Pumping VSD.- Variable Speed Drive

ACKNOWLEDGMENTS We thank PATG and GPEN management authorities for their information and permission to expose it, as well for authorization and support to carry out diverse activities in order to accomplish ALSs diagnostic workshops and complementary activities, and specially to all the persons involved in these events, from all participating work areas in PEP.


REFERENCES Gestin Integral de Sistemas Artificiales de Explotacin (GISAE). Diagnstico, Recomendaciones y Plan de Accin, Docto. Interno de la SGRT-GSPT-PEP. The Increasing Role of Unconventional Reservoirs in the Future of the Oil and Gas Business, Stephen A. Holditch. Schlumberger, SPE/Holditch, dic/2001; Ponencia Ejecutiva sobre avances y escenarios del PATG, Ing. Antonio Narvaez Ramirez, Administrador del Activo, nov-2011. Artificial Lift Management: Recommendations and Suggestions of Best Practices. Hirschfeldt, C. Marcelo. CT&F - Ciencia, Tecnologa y Futuro. Ecopetrol Magazine SPE 124737. Selection Criteria for Artificial Lift System Based on the Mechanical Limits: Case Study of Golfo San Jorge Basin. Hirschfeldt, C. Marcelo, Ruiz Rodrigo.(2009) SPE Annual Technical Conference and Exhibition held in New Orleans, Louisiana, USA. SPE 108054. Artificial-Lift Systems Overview and Evolution in a Mature Basin: Case Study of Golfo San Jorge. Hirschfeldt, C. Marcelo , Distel, F., Martinez, P.(2007) SPE Latin American and Caribbean Petroleum Engineering Conference held in Buenos Aires, Argentina. Artificial Lift Experience in Mature Fields Case Study Golfo San Jorge Basin. Hirschfeldt, C. Marcelo. (2006). ARTIFICIAL LIFT CONFERENCES . Jakarta, Indonesia Recommendations and Comparisons for Selecting Artificial Lift Methods. Clegg, J.D., Bucaram, S.M. & Hein, N.W. (1993). J. Petrol. Tech.


ANNEX A GRAPHICS AND FIGURES

Fig. 1 Golfo San Jorge Basin, Argentina Fig.2 - Chicontepec Project, Mxico

Fig. 3 Contrast PEP-AIATG (activity levels). Fig. 4 Sectors/Fields distribution