23rd World Gas Conference, Amsterdam 2006

GEOTECHNICAL MONITORING AS A BASIS FOR PROVIDING OPERATIONAL RELIABILITY AND SAFETY OF OIL PRODUCING

FACILITIES IN PERMAFROST

A.I. Bereznyakov

Russia

ABSTRACT Hydrocarbon fields in West Siberia’s northern areas are constructed and developed under

extremely complicated geocryologic conditions characterized by distribution of unbound, dispersed and high-iced soils sometimes saline one. Without proper geotechnical support of engineering facilities at the design, construction and operation/ development stages, the most unfavorable conditions of the geo-engineering environment could lead to a large-scaled deformation of field structures, facilities, equipment and pipelines in the course of their operation, which, in its turn, could cause equipment failures, accidents and material loss of assets.

Long-term experience in comprehensive scientific and industrial R&D shows that effective

operation of gas producing systems can be provided only in case if sufficient and prompt information on the system status at all its life stages is available. This requirement was a precondition for arranging a system monitoring at Nadymgazprom’s fields, with a geotechnical monitoring as an integral part of such a system; the above said geotechnical monitoring is determined as a scope of work including: monitoring over geotechnical systems (engineering facilities, surface boundary layer and surrounding permafrost); storage, processing and interpretation of data acquired; prediction and management of the stability of engineering facilities’ substructures and foundations and embedding geo-engineering environment. The objective of geotechnical monitoring is to ensure stability and industrial safety of gas producing facilities at all stages of their service life, minimize man-caused harmful impact on the environment, and optimize expenditures of investors and oil & gas producing companies on construction and operation of all types of engineering facilities in permafrost.

At Nadymgazprom, geotechnical monitoring is integrated in a unified filed facilities’

management system and allows us to ensure continuous failure-free operation, revise engineering solutions related to the construction of substructures and foundations of newly-designed and upgraded field facilities as well as significantly improve profitability.

This report describes an example of practical implementation of the geotechnical monitoring

system at producing well design stage for the Bovanenkovskoye oil and gas condensate field. The concept of providing producing well reliability through specialized geocryologic survey, thermal behavior prediction and industrial experiment for especially complex geocryologic conditions is presented herein.

TABLE OF CONTENTS

Abstract 1. Introduction 2. Geotechnical monitoring technology

2.1. Structural diagram modules 2.1.1. "Monitoring" circuit modules 2.1.2. "Control" circuit modules

3. Implementation of geotechnical monitoring technology in gas producing company’s

business activity

3.1. Preliminary survey stage 3.2. Behavior monitoring during construction 3.3. Behavior monitoring during engineering facility operation

4. Geotechnical support of producing wells at the Bovanenkovskoye oil and gas condensate

field 5. Conclusion 6. References 7. List of Figures

1. INTRODUCTION

Since the early 1970s, large gas, gas condensate and oil fields have been explored and developed in the northern part of the West-Siberian region. This region is characterized by permafrost occupying virtually the whole area. The experience in constructing and developing hydrocarbon fields under extremely unfavorable geocryologic conditions is unique. Technogenic impact on permafrost, which exceeds the stability limits of natural complexes, predetermines the development of destructive processes which often diminish the bearing capability of engineering facility substructure’s soils. While conducting business in northern regions, environmental issues become acute. Longstanding experience in comprehensive scientific and industrial R&D shows that effective operation of gas producing systems can be provided only in case if sufficient and prompt information on the system status at all its life cycle stages is available. This circumstance was a reason for arranging system monitoring at Nadymgazprom’s fields, i.e. the development of monitoring fundamentals, procedures and technologies, and the implementation of the above mentioned technology in practical activity of gas producing companies [1]. This report describes a geotechnical monitoring (monitoring of geotechnical systems) which is an integral part of system monitoring and ensures operational safety of gas producing facilities in West Siberia’s northern areas.

Any gas producing facility interacting with permafrost is considered a geotechnical system. At

the same time, thermal and mechanical interaction of a facility with geological environment is considered as a multidimensional nondeterministic process passing over time. If output parameters of a process do not reach their limit values (e.g., values of load transferred onto a substructure, and of maximum allowable deformation), than the quality of the system deems intact; otherwise, the quality is supposed to be deteriorated, and the system fails [2].

Geotechnological systems have the following features which distinguish them from other gas

producing systems: - geotechnical system is not included in the geotechnological system of gas production by a

formal attribute of a target process; - during the interaction of such subsystems as “wells”, “gas gathering system loops”, “booster

compressor stations – complex gas treatment units", or “interfiled gas gathering pipeline” with an external medium, the thermal interaction of gas producing facilities with permafrost is of utmost importance;

- loss of geotechnical system stability could have catastrophic consequences for any of the

above mentioned subsystems and for gas producing system as a whole; - parameters characterizing geotechnical system both refer to gas producing facilities and

external medium of geotechnological system; - block of geotechnical system monitoring is the only one of all local monitoring blocks

responsible for control over parameters of gas producing facility’s interaction with permafrost, which provide stability and trouble-free operation of the geotechnological system;

- structures, surface boundary layer parameters and part of permafrost zone are subject to

surveillance; the surveillance radius is determined individually for each geotechnical system; - information acquired in the course of monitoring is taken into consideration during the

operation of all functional subsystems while implemented technical approaches influence the possibility of reaching the targets by all previously determined local monitoring blocks.

The objective of geotechnical monitoring is to provide stability and industrial safety of gas

producing facilities at all stages of their service life, minimize man-caused harmful impact on the environment, and optimize expenditures of investors and oil-and-gas producing companies on construction and operation of all types of engineering facilities in permafrost.

2. GEOTECHNICAL MONITORING TECHNOLOGY

To pursue the objective, the technology of geotechnical monitoring was developed (ref. to structural diagram on Fig. 1).

2.1. Structural diagram modules Schematics of geotechnical monitoring includes surveillance and control circuits and

corresponds to the control-predictive monitoring principle applied in many up-to-date researches, but, at the same time, it has a number of peculiarities and fundamental dissimilarities making it more comprehensive and demonstrative. The visibility reflects qualitative change in information while passing from one diagram module to another.

2.1.1. "Monitoring" circuit modules 1. "Surveillance Facilities ". Facilities subject to geotechnical monitoring are determined and

classified in this module. 2. "Network and monitoring procedure". Surveillance network comprises a system of

thermometric wells, geodetic data and marks. Monitoring procedure includes a list and regularity of monitoring activities.

3. " Surveillance data processing and explication". In this module, the monitoring data are

generalized and sieved; information is classified and processed. At the outlet of this module, the array of controlled parameters is a result of monitoring over a certain period of time.

4. In the "Dynamic data base" module, initial information characterizing geotechnical system status (including design parameters and simulation results) is accumulated and stored. Data arrays with information on facilities for surveillance period are formed in this module. This information forms spatial-temporal multidimensional ranges for surveillance facilities. Some information is stored in order to generalize operational experience or to be used at later service life stages; this information goes to the "Normative information…" module.

2.1.2. "Control" circuit modules The technology presented herein combines monitoring and control for the following reasons. If

the “monitoring” and “control” circuits are not united in one loop, managerial decision-making could be of a conjunctive nature. The possibility of decision-taking on a real-time basis is of not less importance.

Within the frames of the "Control" circuit, science-based decisions are developed, which

ensure operational reliability of facilities’ substructures and foundations, including control of thermal and humidity conditions of substructures’ soils and revision of design approaches to foundations and supports of engineering facilities. The controlled elements are influenced only in case if information acquired during monitoring is available.

5. " Normative information …" To perform control functions, monitoring is bolstered by a

system of scientifically substantiated standards which have both technological and environmental meaning; for performing predictive functions, monitoring is supported by a system of optimized (adequate) models. This module, in particular, includes a model of heat interaction between gas producing complex and permafrost zone. It also includes registered data bases, software packages, and innovative activity results, prepared in the form of industrial R&D reports, procedures and patents for inventions.

6. "Review of results, simulation, prediction". Based on the study of monitoring results, the

state of system elements is controlled and dynamics of geocryologic processes is predicted. At the same time, prediction should take into consideration changes caused both by natural and technogenic factors.

7. "Development of technical measures to control thermal behaviors". Based on the results of

the geotechnical system condition monitoring, prediction and simulation, scientifically justified decisions are taken and practical initiatives are developed to:

- eliminate hazardous or undesirable short or long term changes in geo-engineering

environment; - eliminate and avoid unacceptable conditions of geotechnical systems: increased stability of

building, structure, equipment and pipeline foundations; prompt warning of maintenance departments of unacceptable deformation development, and elimination of failures identified.

8. "Controlling facilities". Controlling facilities are used to control soil condition of substructures

and engineering facilities. Controlling actions maintain the stability of facilities and thus allow pursuing the monitoring

objective.

3. IMPLEMENTATION OF GEOTECHNICAL MONITORING TECHNO LOGY IN GAS PRODUCING COMPANY’S BUSINESS ACTIVITY

The technology of geotechnical system monitoring in permafrost, implemented in

Nadymgazprom’s business activity, includes the following surveys: study of natural (background) geocryologic engineering conditions on a construction site; development of behavior surveillance procedures for construction and operation of gas producing complex’s engineering facilities; monitoring of soil conditions of gas producing facilities’ substructures and adjacent areas; control over foundation, support, equipment and pipeline stability; monitoring of equipment and pipeline

deformation, strain-stress state and vibration; discrepancy identification for parameters characterizing status of geotechnical system components and geotechnical system as a whole; prediction of changes in and condition of geocryologic systems. Surveillance facilities represent different types of geotechnical systems – areal and linear structures, producing wells located in northern fields of West-Siberia, etc.

Maximum efficiency of geotechnical monitoring is achieved if this monitoring is performed at

the facility design, construction and operation stages. Thus, monitoring is a three-staged procedure: preliminary survey, behavior survey during construction, and control of operational facility conditions.

3.1. Preliminary survey stage Natural engineering-geocryologic conditions of expected construction site are explored to

study natural background. To this end, data of all preliminary studies for this area are used. To develop deformation tolerances, a special program is implemented. Within the framework

of this program, design procedures and control methods are developed and key parameters for the main equipment and pipelines employed in the gas industry are determined. These design procedures and control methods form a basis for design.

The preliminary survey outcome is as follows: - creation of geocryologic engineering model of substructure soil profile, development of

behavior surveillance system for facility construction & operation stages and effective revision of field construction projects;

- preliminary prediction of substructure soil behavior forming a basis for critical analysis of

design approaches; - substantiation of admissible building, equipment and pipeline vibrations & deformations. 3.2. Behavior monitoring during construction The monitoring network makes it possible to identify destructive geocryologic processes at

construction sites. Control of how builders fulfill project requirements is performed jointly with a designing

company. Upon the completion of the gas industry facility construction, non-destructive tests are

conducted to determine stress-strain state of equipment and pipelines, and detailed leveling of buildings, equipment and pipelines is conducted. All parameters obtained are recorded in a facility’s geotechnical certificate.

3.3. Behavior monitoring during engineering facilit y operation At this stage, comprehensive monitoring over geotechnical system condition is underway:

instrumentation survey of geocryologic process dynamics of operational facility’s substructure soils, and examination of stability of foundations and substructures; diagnostics of above-foundation structures’ condition. Measuring data are processed and accumulated in data bases and are then used for controlling the development of geotechnical system condition trends as well as for revision of predictive assessments. Based on the prediction programs and updated actual data, mathematical models of thermal state of operational structures and facilities’ substructure soils as well as models of stress-strain state of equipment and pipelines are developed. The above mentioned mathematical models are continuously clarified based on data incoming from subsequent monitoring; this allows us to predict changes in the geotechnical system state. The prediction enables us to timely receive information on undesired or hazardous changes and promptly develop recommendation on how to fix the problems [3].

At this stage, besides the control over geocryologic process dynamics, technical condition of foundations, supports, buildings, equipment and pipelines is monitored by behavior performance leveling via special network of stationary observation marks in accordance with approved schedule.

Behavior monitoring data are processed and recorded in a respective data base. The review

of results allows us to take prompt measures to eliminate unacceptable deformations of buildings, equipment and pipelines; identify and neutralize (prevent) unfavorable trends in the deformation development dynamics; reasonably determine the necessity, sequence and main technical approaches to refurbishment and repair of “zero cycles” of field facilities.

4. GEOTECHNICAL SUPPORT OF PRODUCING WELLS AT THE BOVANENKOVSKOYE OIL AND GAS CONDENSATE FIELD

As an example of successful implementation of the concept of providing field facility reliability

under extremely complex geocryologic conditions of West Siberia’s northern part based on geotechnical monitoring at Nadymgazprom, let’s consider geotechnical support of producing wells at the Bovanenkovskoye field (Yamal Peninsula) at the design stage.

The necessity of taking into account the consequences of producing wells’ thermal influence

on imbedding permafrost is a specific feature to be considered while constructing and developing fields in permafrost zone. A cylinder-shaped defrosting zone, with 3-4 to 10-12 m in radius (dependent on producing fluid temperature and flow rate, well design; composition, properties and temperature of embedding soils), is formed around the well. In the wellhead area, the defrosting zone looks like a cone with a radius of up to 25 m; this shape is produced under joint influence of the well and existing surface conditions. Thawing of permafrost soils sometimes goes along with the development of unfavorable conditions: setting of iced soils with the deviation along the wellbore and transfer of additional loads on it, formation of frost-thaw collapsing cones in the wellhead area, increased soil permeability in the near-well area, etc.

Due to the above mentioned features to be considered during well construction and

development under complex geocryologic conditions of the Yamal Peninsula, the following difficulties can appear:

- deformation of well support casing (subsidence and deviation from vertical position) under

influence of defrosting permafrost soils and own weight under conditions of slight restraint by embedding soils;

- deformation of well cluster caused by frost-thawing process and formation of large-sized

wellhead subsidence cones complicating well development procedure; - deformation of wellhead piping foundations and pipelines due to loss of bearing capability by

soil during thawing in the wellhead zone and temperature increase in negative range; - gas shows from producing horizon and permafrost section in the wellhead area. Nadymgazprom’s specialists have prepared a program of geotechnical support of producing

well construction & development under especially complex geocryologic conditions of the Bovanenkovskoye oil and gas condensate field. The implementation of the program allowed us to:

- develop criteria of standard interaction between well and embedding permafrost soil, which

ensure stability of geotechnical system; - identify different types of geocryologic section in different areas, and study peculiarities of

soil composition, regularities and range of variation of ice content in permafrost soil; - identify clusters with unfavorable conditions for well construction and development,

characterized by high thickness (first tens of meters) of highly-iced soils and thick embedding

reservoirs of ice layers; optimize location of producing well platforms, taking into consideration the territory’s geocryologic profile specifics;

- develop a geotechnical monitoring network schematics which allows us to control thermal

interaction between components of the “well-permafrost” geotechnical system as well as adherence to industrial safety standards.

In addition, during the implementation of the program, engineering solutions for providing

permafrost stability in a wellhead area over the entire well development cycle by using heat insulated tubing and vapor-liquid cooling devices have been developed based on comprehensive geocryologic prediction. Dependent on geocryologic conditions, wellhead and wellbore profile, temperature and flow rate of producing fluid, several typical design approaches to permafrost thermal stabilization were developed. Diagram of permafrost thermal state stabilization in a near wellhead zone of producing wells as well as methods of providing the stability of well and well-embedding permafrost though employment of seasonally-operated vapor-liquid cooling devices is presented in Fig. 2. Fig. 3 shows the implementation of the above mentioned methods during experimental work at the Bovanenkovskoye oil and gas condensate field.

While carrying out industrial experiment on permafrost thermal protection for a producing well

at the Bovanenkovskoye field, the technical feasibility of maintaining well-embedding permafrost over the entire service life of a well and, therefore, of providing the stability of geotechnical system including producing well, piping, well cluster site (earthwork or platform) and near wellhead permafrost was substantiated. Results of predictive assessments of temperature profile dynamics in a near wellhead zone of producing well equipped with heat-insulated tubing and thermal stabilizers in the wellhead zone are given in Fig. 4.

Therefore, the implementation of geotechnical monitoring methods at the design stage

enabled us to resolve a wide range of issues on providing the stability of producing wells under extremely complex geocryologic conditions of the Bovanenkovskoye field.

5. CONCLUSION The implementation of the geotechnical monitoring technology in Nadymgazprom’s business

activity has brought the following results. 1. Trouble-free operation of producing facilities at the Medvezhye field, a pioneering field in

West Siberia’s northern areas. A network of monitoring surveillance embracing all of the main engineering facilities of gas producing complex – wells, process pipelines, gas treatment facilities used to prepare gas for transportation – was arranged and is in operation today. Geotechnical monitoring allows us to timely develop science-based technical approaches to refurbishment of field facilities’ substructures and foundations and to take necessary managerial decisions to prevent accidents.

2. Based on the monitoring results, engineering solutions on constructing substructures and

foundations for complex gas treatment units at the Yubileynoye and Yamsoveiskoye fields and booster compressor station at Yubileynoye were revised. This enabled us to improve the efficiency of investments in facility construction, reduce workover expenditures and significantly diminish the probability of failures.

3. The gas industry’s regulations on arranging and conducting geotechnical monitoring at

newly designed, constructed or operational facilities in permafrost area. Starting with justification of investments in construction of promising fields on the Yamal Peninsula and later on – a the design stage, the design documentation includes the development of the geotechnical monitoring network.

4. Experience in conducting geotechnical monitoring and the results of this monitoring allowed

us to develop and implement a number of innovative solutions protected by the RF patents which are designed to ensure the stability of engineering facilities’ foundations in permafrost, stability of producing wells, reduces foundation construction costs and increase profitability of investment projects.

5. The issues of providing operational reliability of civil construction facilities were successfully

resolved. Taking into consideration complicated natural and climatic conditions of the region and limited regional funds, this issue is of paramount social importance.

6. Total savings due to implementation of innovative technical approaches over the last three

years amounted to over USD 15⋅106. 7. The technology of geotechnical system monitoring in permafrost described herein is a

universal tool applicable to any engineering facility of the oil and gas industry, at different stage of its service life (design, construction, development/ operation, abandonment). Practical implementation of this technology allows us to successfully consider and tackle the whole spectrum of issues faced by gas producing companies and by the region while constructing engineering facilities in permafrost. By employing adapted up-to-date procedures, a limited, properly trained staff is able to control key components of engineering facilities of a large diversified enterprise or a region.

8. The technology developed and tested in the region can be successfully employed for

implementation of large-scaled investment projects in any permafrost area (West and East Siberia, Yakutiya, Chukotka, etc.).

6. REFERENCES 1. Technology of system monitoring over gas producing facilities located in West Siberia’s

northern areas/ А.I. Bereznyakov, Ye.I. Bereznyakova, О.М. Yermilov, V.I. Kononov // Gazovaya Promyshlennost. – 2005. – №9. – Pages 21-24.

2. L.N. Khrustalev. Application of reliability theory to engineering geocryology tasks// Kriosfera

Zemli. – 1997. – Vol. 1. – № 2. – Pages 12-17. 3. Prediction of producing well’s thermal influence on permafrost at simultaneous-individual

operation of two facilities at the Bovanenkovskoye oil and gas condensate field/ L.S. Chugunov, А.I. Bereznyakov, Z.S. Salikhov, А.P. Popov, А.B. Osokin, G.К. Smolov // Issues of methodology and advanced technologies for natural gas filed development : Treatise reports – М.: VNIIGAZ, 1996. – Part 2. – Page 159-174.

7. LIST OF FIGURES

Fig. 1. Geotechnical system monitoring diagram Fig. 2. Engineering approaches to permafrost thermal state stabilization in a producing well’s wellhead area Fig. 3. Practical implementation of thermal protection methods for producing wells Fig. 4. Results of predictive assessments of thermal field dynamics