GEOTHERMAL DRILLING PRACTICES AND GUIDELINE INDONESIA SHALLOW AND DEEP GEOTHERMAL WELLS

FOREWORD:

It is through the dictate of the ________________and the efforts of _____________that this geothermal well drilling practices and guideline is developed to ensure that safety of personnel and equipment, environmental protection and good drilling operation practices are followed and seriously implemented to be able to attain an efficient and cost effective geothermal well.

Through the geothermal drilling experience of the people involved in the development of this guideline, some of the oil and gas practices have been modified to suit the needs of a geothermal drilling operation.

This covers site preparation, well planning and design, drilling and well abandonment. It is recommended that this guideline which has considerable data based on experience should be followed so that a geothermal well can be drilled and operated safely.

GENERAL

1 Well Planning and Design:

1.1 Data acquisition, review and analysis

The quality and completeness of data acquired is vital to the success or failure of a geothermal well. To start with, the geothermal scientific group proposes to drill a well. That proposal should indicate elements relevant to the well being proposed. A checklist should be prepared indicating the well objective, i.e. exploration well or development well or appraisal well or work over. It should likewise indicate timeframe i.e. desired spud date and the area where the well will be drilled.

1.2 Well Design

The well design defines casing specification i.e. size, grades, weights, connection type and setting position relative to depths. It also defines the directional requirements, wellhead completion assembly, drilling fluid specification, completion method, BOPE assembly and cementing requirement/method.

1.2.1 Evaluate all the acquired data1.2.2 List down all potential drilling problems to be able

to have a starting point in the design of casing string.

1.2.3 Confer with the geologist and reservoir engineers and discuss likely scenarios pertaining to formation temperature, fluids in the formation and rock types and take note of the of the new inputs that is necessary in the preparation of the program.

1.2.4 Select appropriate casing setting depth, casing specifications taking into account kick tolerances to avoid or prevent drilling problems. It is recommended that a conservative design be adopted as errors can occur in the prediction of formation characteristics.

1.2.5 Design the cement slurry that will be appropriate based on data gathered.

1.2.6 Specify the wellhead completion assembly.

1.2.7 Ensure that all items in the proposal are considered and the design meets the requirement and discuss with the proponent.

1.2.8 Circulate the design to all departments concerned and seek approval.

1.2.9 Prepare cost estimates (particularly called the AFE).

1.2.10 Prepare the drilling program1.2.11 Prepare time and depth curve.1.2.12 Identify items required that need long lead time

and proceed ordering these items.1.2.13 Determine rig availability and define start of

operation.

2. Choice of site location:

The determination of the location must take into consideration the result of geological evaluation of the subsurface area and make certain that it is of high integrity to support the rig equipment and not susceptible to wash out and erosion due to run-off water and flow of ground water and possible prevention of a blowout when the well comes under pressure at shallow depth. Also the site should be stable in the long term, even after the rig has completed the drilling and already pulled out of the area.

3. Site preparation and Designing the site location

The design of the site should take into consideration the size and tonnage of the rig that will be utilized in the drilling operation. It should be able to support the dead loads and dynamic loads carried by the substructure. Likewise the size of the location should consider the safe maneuverability of truck loaded with rig equipment during rig up/rig down.

3.1 Fill surface should be compacted with appropriate surfacing materials and protected from erosion.

3.2 Provide appropriate drainage all around the location.

3.3 Surfacing materials should be of good quality to provide all weather access.

4. Consolidation grouting of location:

Proper assessment should be done on whether the site should be grouted. It may be necessary to drill small probe hole to find out and assess permeability of the formation within the first 100 feet from the surface. Consolidation grouting may reduce or avoid shallow circulation losses during drilling. It also consolidates loss formation thereby improving the load carrying capacity of the shallow formation. It may also divert the flow of formation fluid or gas away from the immediate vicinity of the rig in case of a shallow blowout. The grout holes should be drilled immediately below the drilling equipment. 4.1 Required Equipment

-Small unit rig that can drill about 3 inches hole diameter to about 150 feet with pump that is capable of pumping about 100 psi.

- Cement batch mixer-- Drill rods.

4.2 Type of cement required

- Class A cement – A cement slurry without any additive would suffice for this type of activity.

4.3 Grout holes required

- Drill 5x 2 to 2 ½ inches holes starting from the center of the cellar.

- The first hole shall be drilled to TD of 100 feet.

- The 4 satellite holes (about 10 to 20 feet from cellar center depending on the slurry take of the first hole) shall be drilled to 75 feet.

4.4 Grouting procedure

- Drill to about 20 feet. Pump the cement slurry and until refusal with about 15 psi.

- After waiting on cement for about 6 to 8 hours drill out the cement column and proceed to drill to 40 feet. Pump the cement slurry and until refusal with about 32 psi.

- After waiting on cement for about 6 to 8 hours drill out the cement column and proceed to drill to 60 feet. Pump the cement slurry and until refusal with about 48 psi.

- After waiting on cement for about 6 to 8 hours drill out cement column and proceed to drill to 80 feet. Pump the cement slurry and until refusal with about 65 psi.

- After waiting on cement for about 6 to 8 hours drill out cement column and proceed to drill to 100 feet. Pump the cement slurry and until refusal with about 80 psi.

Notes: - If the intake of the hole is excessive or more than what is prescribed in the procedure, the concerned parties i.e. geologist and project management should be consulted so that appropriate action can be taken.

-Additional holes may be required if the slurry intake is more than what is prescribed. In this case the grouting procedure should be followed.

-Caution should be taken not to fracture the formation because of overpressure.

- If the hole intake of slurry is more than the hole capacity and refusal pressure, drill another grout hole near that hole following the same procedure.

4.5 Activity report (grouting)

A report should be prepared indicating hole number and size, slurry mix, slurry density and volume, depth, pressure and any loses encountered during drilling and slurry pumping.

5. Cellar construction

The size of the cellar shall be constructed with consideration to:

- Proper clearance of BOPE to be installed during drilling.

- Dimension of the substructure of the rig that will be utilized.

- Safety of personnel who work in the cellar.

- Appropriate space for production wellhead.

- Drainage.

- Size of conductor pipe which will buried/drilled to about 10 feet to 15 feet.

6. Waste sump:

A waste sump should be built in the vicinity of the rig where cuttings, waste mud, waste oil; excess cement slurry shall be dumped as necessary. This is to ensure protection of the environment and ease of operation. The size of the sump shall be between 2500 cubic meters to 3000 cubic meters. Detailed drawings will be provided. If building a waste sump is not practical, inappropriate for the location or there are lease restrictions to build such, an alternative method of protecting the environment is to resort to close lope system where the liquid waste or discharge can be managed effectively. Check with companies that provide this kind of service.

7. Water supply:

The water supply volume should be between 800 gpm to 1200 gpm depending on the category of the hole to be drilled whether regular hole or big hole. The water should be analyzed for all its elements to ascertain its quality and

avoid drilling operations problems which may be caused by elements that is detrimental to the operation.

8. Casings

Various sizes of casings shall be used for the purpose of protecting ground and surface waters, the environment, safety consideration and ensure or provide adequate control of the well during drilling and production. Numerous books are available as reference in the design of the casing. Pressure and temperature should be considered in the casing design. The casing should be able to withstand thermal stresses in the cemented section and uncemented section of the hole during drilling operation or production of the well.

Casing design should consider formation characteristics such as loss circulation, formation caving, formation acidity, formation pressure and temperature and fracture gradient.

8.1 Conductor pipe

This is normally used to carry drilled cuttings to the surface when drilling the top portion of the well and where a diverter will be installed. This is usually 30 inches in diameter and driven/cemented to about 10 feet from the surface. This is installed during the construction of the cellar.

8.2 Surface casing

In a geothermal well this is the first set of casing where a blowout preventer can be installed. This protects fresh water aquifers from contamination and it isolates the shallow unconsolidated portion of the well. For a normal geothermal well this size is 20 inches. For big holes this size is 22 inches. The casing should be cemented up to the surface with a slurry mix that will be formulated using class g cement and additives. Refer to cementing topic.

The setting of the casing should be deep enough so that formation fracture pressure is high enough for the well to be closed in on a kick while drilling for the next casing string.

8.3 Intermediate casing

This type of casing is also called the anchor casing. This increases the pressure integrity of the well so that it can be deepened. The depth on which the shoe of the intermediate casing is set is dependent on the structural competence of the formation and safe drilling conditions until the expected or calculated depth of the production is set and cemented to surface. It is in this section that the casing head flange (CHF) is installed for a higher rating BOPE and where the production wellhead is put in place after completion of the well.

8.4 Production casing

This is the casing string that is exposed to the formation fluid when the well is discharged for production. It is very important that this is properly cemented to surface and free of any defect as this the permanent pipe that is always exposed to production fluid. The designer should bear in mind that this casing will be exposed to severe condition during production and has been exposed to mechanical wear during drilling operation. It is prudent for the designer to consider all data available in coming up with the correct grade, weight and connection of the casing. A failure in the design of the casing is a failure of the well.

8.5 Production slotted or perforated liner

This is the string of casing installed to protect the hole from collapse of the formation. Production fluid passes through the perforation during discharge of the well. The setting depth of the liner is dictated by the geologist, after conferring with department concerned.