Pre-feasibility report

Transcription

1 Pre-feasibility report 1. Introduction The Banskandi PML, Bhubandar PML, Sector VC PML and Adamtila Extension PML of Cachar and Karimganj district in Assam was awarded to ONGC on 21/07/1997, 22/12/2002, 30/11/2014 and 03/03/2012 under the long term PML of 20 years. ONGC has applied for regrant of Banskandi PML on The proposal is under review of DGH. Based on the analysis of G&G data acquired in the area, leads had been identified in Banskandi and Bhubandar PML blocks. 2. Details of PML Block: 2.1 Banskandi PML: The Banskandi PML covers an area of 15.0 SKM. The structure was proved hydrocarbon bearing by its first well BK-1 drilled in the year Till now, total 13 wells have been drilled, out of which only three wells BK-1, 2 and 6A are bearing hydrocarbon. Rest of the wells are either dry or abandoned. The Banskandi structure is a concealed high and is a part of the frontal folded belt of Assam Arakan Geosynclines. It is a doubly plunging anticline trending NE-SW in the north and NNE-SSW in the south and follows axial trend of Pathimara anticline to the northeast and Rengte anticline to the south-west. The structure is bounded by two reverse faults on either sides and later affected by WNW-ESE trending cross fault, thus dividing the structure into sub-blocks. The structure is flanked by Silchar syncline to the west and Labak syncline to the east. Banskandi area are mostly alluvium covered except for small patches of Dupitila outcrop to the north, west and south of the structure. The coordinates of the Banskandi PML boundary are: A 24⁰ ⁰ B 24⁰ ⁰ C 24⁰ ⁰ D 24⁰ ⁰ E 24⁰ ⁰ F 24⁰ ⁰ G 24⁰ ⁰ A 24⁰ ⁰ Bhubandar PML:

2 The Bhubandar PML covers an area of 6.0 SKM. Three wells have been drilled in the Bhubandar PML area, out of which two well i.e, BU-2 and BU-6 are gas producer. It is believed that neighbouring Labak syncline acted as kitchen for Bhubandar field. The well BU-1 was terminated at 3684m against a target depth of 4500m. A gas bearing sand (S-1) in Upper Bhuban Formation could not be tested due to technical constraint. Subsequently, BU-2 was drilled from the same location and was tested gas bearing. Apart from this S-1 sand, another sand S-2 in Upper Bhuban Formation is identified as gas bearing on log and gas in place of possible category has been calculated. The concealed high of Bhubandar structure located to the southern part of Labak syncline was identified on the basis of Geomorphological studies and later confirmed by seismic as well as gravity, magnetic and photo geological data. It appeared to be an en-echelon extension of Teidukhan anticlines which boarders its south eastern part and also bounded by NE-SW trending Rengte anticline towards west. The coordinates of the Bhubandar PML block boundary are: A 24⁰ ⁰ B 24⁰ ⁰ C 24⁰ ⁰ D 24⁰ ⁰ A 24 ⁰ ⁰ Sector VC PML: Five exposed structures falling in the Sector VC PML covering an area of SKM, are Masimpur-Indernagar, Rangamati, Pathimara, Tukbai (Dalichara) and Digli. Tukbai structure has been proved as gas bearing based on results of well TK-3A. Masimpur & Pathimara structures have given gas indications on drilling in wells MS-1&2 and PM-2&3. In Tukbai structure Upper Bhuban play is proved in well TK-3A and to prove the extension of this Upper Bhuban play. In Masimpur structure, well MS-1 showed light oil during drilling of Bhuban Formation and in well MS- 2 presence of gas during testing of Bhuban Formation was observed. Anticlines within the block are separated by broad intervening synclines and are considered to be the kitchen for hydrocarbon generation. The structural trend of Pathimara structure extends upto the established gas field Banskandi to the south. Surface gas seepages are reported in the eastern side of Labak Syncline which separates Tukbai & Pathimara Structures. The coordinates of the Sector VC PML boundary are: A 24 ⁰ ⁰ B 24⁰ ⁰ C 24⁰ ⁰

3 D 24 ⁰ ⁰ E 24 ⁰ ⁰ F 24 ⁰ ⁰ G 24 ⁰ ⁰ H 24 ⁰ ⁰ A 24 ⁰ ⁰ Adamtila and Adamtila Extension PMLS: In the Adamtila and Adamtila Extension PML which has an area of 4.0 SKM and SKM respectively, the Langai anticline is a doubly plunging, narrow elongated, tightly folded, cross faulted anticline having N-S to NNE-SSW trend with steep limbs. It is lies east of Adamtila Gas Field and north of discovered Khubal gas field. The Champabari syncline in the west of this area has acted as a proved kitchen. The Langai structure is bounded by N-S trending longitudinal fault and is also traversed by few prominent younger cross faults. Therefore all elements of hydrocarbon generation, charging and entrapment are present around whole of the anticlinal area. The core of the anticline exposes Upper Bhuban rocks. Younger formations like Tipam and Dupitila are exposed in the flanks. Two wells were drilled in Langai anticline both gave gas indication from Bokabil and Bhuban reservoirs. The coordinates of the Adamtila Block boundary are: A 24⁰ ⁰ B 24⁰ ⁰ C 24⁰ ⁰ D 24⁰ ⁰ A 24⁰ ⁰ The coordinates of the Adamtila Extension Block boundary are: A 24 ⁰ ⁰ B 24 ⁰ ⁰ C 24 ⁰ ⁰ D 24 ⁰ ⁰ E 24 ⁰ ⁰ F 24⁰ ⁰ G 24 ⁰ ⁰ H 24 ⁰ ⁰

4 I 24 ⁰ ⁰ J 24 ⁰ ⁰ K 24⁰ ⁰ L 24 ⁰ ⁰ M 24 ⁰ ⁰ N 24 ⁰ ⁰ O 24 ⁰ ⁰ P 24 ⁰ ⁰ Q 24 ⁰ ⁰ R 24 ⁰ ⁰ S 24 ⁰ ⁰ T 24 ⁰ ⁰ U 24 ⁰ ⁰ V 24 ⁰ ⁰ W 24 ⁰ ⁰ X 24 ⁰ ⁰ Y 24 ⁰ ⁰ Z 24 ⁰ ⁰ A1 24 ⁰ ⁰ A2 24 ⁰ ⁰ A3 24 ⁰ ⁰ A4 24 ⁰ ⁰ A5 24 ⁰ ⁰ A6 24 ⁰ ⁰ A7 24 ⁰ ⁰ A 24 ⁰ ⁰ Based on the prospectivity in the PML Blocks, it is proposed for environmental clearance for drilling of thirty three exploratory/development/production wells in five onshore PML blocks in AAFB, A&AA Basin, Cachar District and Karimganj District, Assam to probe the envisaged prospects for hydrocarbon. 3) Planned Activities: After grant of environment clearance, mostly revenue land or agricultural land will be acquired on temporary lease. This will be followed by civil work and hardening of drill-sites and if required, preparation of approach roads. Around 1.10 hectares of land (100m x 110m) is required for each drill-site which will host temporary shades for equipment and personnel, foundations for drilling rigs and heavy equipments, cellar pit, waste water pit and diesel tanks. The land will be acquired on a temporary basis and if commercial quantity of oil or gas is found, the land will be taken on long lease and if oil and gas is not found in commercial quantities, the land will be returned to the owner by bringing back to its original status and adequate compensation as per the guidelines of local administration will be provided. The trajectory of well course will depend on the availability of land above the sub-surface position. A vertical well will be planned if land is available above the planned sub-surface position,

5 else a deviated well will be planned. The planned depths ranges from m for exploratory wells and 2500m for development wells. However +300m variation in depths may be possible depending on the depth of discovery. Based on the discovery at exploratory wells to be drilled, development wells are planned in Banskandi, Bhubandar, Sector VC, Adamtila and Adamtila Extension PML s. Development/Production wells of Southern part of Banskandi field and that of Bhubandar fields will be connected to Banskandi-Bhubandar Pipeline. This Banskandi-Bhubandar pipeline will be connected to Banskandi GCS. Development/Production wells for Northern part of Banskandi and Sector VC will be connected to Banskandi EPS located at North Banskandi which is under production. The development/production wells from Adamtila and Adamtila Extension PML will be connected to Adamtila GCS which is under production. All the development wells will be connected to the existing facilities and no additional facility will be constructed except connecting the development wells to the existing facilities 3.1 Details of the drilling rig proposed to be deployed Type of rig Drilling mud composition Power generator type and no s Diesel consumption Qty. of fresh water requirement & source Manpower on rig Material requirement & Mobilization Details of solids handling system Details of sewage treatment facility, if any Not applicable Waste pit availability & size 30m X 20m X 1.5m 30m X 20m X 1.5m 40m X 30m X 1.5m Electrical rig Water based drilling fluid AC-SCR type. Six numbers 200 litres/hour m 3 /day. To be transported from nearby source through contractor. 30 person / 12 hrs. shift From ONGC Base, Srikona, Silchar Shale shakers GPM capacity De-sander GPM capacity Desilter-1200 GPM capacity 3.2 Drilling Operations Only water based drilling mud will be used. The quantity of drill cuttings generated will be around m 3 depending on well depth. The quantity of wastewater produced will be about m 3 /day. The rig will be provided with solids handling system comprising Shale shakers (1200 GPM), De-Sander (1200 GPM) and De-Silter (1200 GPM) and Degasser. Drilling operations will be carried out using an electrical type drilling unit for drilling of oil and gas wells. It consists of a derrick, at the top of which there is a crown block and a hoisting block with a hook. From the swivel a Kelly stem is suspended passing through a square or hexagonal Kelly bush which fits into the rotary table. The rotary table receives the power to drive it from an electric motor. The electric motor rotates the rotary table which passes through the Kelly bush and the rotations are transmitted to the bit as the drilling

6 progresses, the drill pipe in singles are added to continue the drilling process. At the end of the bit life, the drill pipes are pulled out in stands and stacked on the derrick platform. A stand normally has 3 single drill pipes. After changing the bit, the drill string is run back into the hole and further drilling is continued. This process continues till the target depth is reached. During the course of drilling, cuttings are generated due to crushing action of the bit. These cuttings are removed by flushing the well with duplex/triplex mud pumps. The mud from the pump discharge through the rotary hose connected to stationary part of the swivel, the drill string and bit nozzles. The mud coming out of the bit nozzles pushes the cuttings up hole and transports them to the surface through the annular space between the drill string and the hole. The mud not only carries away crushed rock from the bottom of the hole but it also cools the bit as it gets heated due to friction with formation while rotating. The mud also helps in balancing subsurface formation pressures and by forming a cake on the walls of the well diminishes the possibility of crumbling or caving of the well bore. At the surface, the mud coming out from well along with the cuttings falls in a trough, passes through the solids control equipments i.e. Shale shakers, De-Sander and De-Silter. These equipments remove the solids of different sizes which get mixed with the mud during the course of drilling. The cleaned mud flows back to the suction tanks to be again pumped into the well. The drilling mud/fluid circulation is thus a continuous cyclic operation. The most suitable clay for mud preparation is bentonite which is capable of forming highly dispersed colloidal solutions. Various other chemicals are also used in mud preparation as per requirements dictated by the temperature/pressure conditions of the wells. The mud is continuously tested for its density, viscosity, yield point, water loss, ph value etc. to ensure that the drilling operations can be sustained without any down-hole complications. 3.3 Drilling Facilities Drilling is a temporary activity which will continue for about 6-9 months for each well in depending on target depth. The rigs are self-contained for all routine jobs. Once the drilling operations are completed, and if sufficient indications of hydrocarbons are noticed while drilling, the well is tested by perforation in the production casing. If the well is found to be successful hydrocarbon bearing, it is sealed off for future development. If no commercial hydrocarbon is struck the well is abandoned according to existing safety norms. 3.4 General Requirements of Drilling Exploratory and development drilling programme requires the following common facilities: a. Drilling muds Drilling of wells requires specially formulated muds which basically comprise inert earth materials like bentonite, barite in water with several additives to give mud weight, fluidity and filter cake characteristics while drilling. The drilling muds have several functions like lubrication and cooling of the drill bit, balancing subsurface formation, bringing out the drill cuttings from the well bore, thixotropic property to hold cuttings during non-operations, formation of thin cake to prevent liquid loss along well bore etc. Several additives are mixed into the mud system to give the required properties. Water based mud will be used to the possible extent in exploratory and development drilling but use of synthetic based mud may require due to complexities associated with the geological formations and associated hole stability problems. b. Power Generation The drilling process requires rotation of drill bit through the draw works which require power. The power requirement of the drilling rig will be met by using the four diesel

7 generator sets with a diesel consumption of about 6 Kl/day. The exhaust stacks of the DG sets are likely to vent the emissions. c. Water requirements The water requirement in a drilling rig is mainly meant for preparation of drilling mud apart from washings and domestic use. While the former consumes the majority of water requirement, the water requirement for domestic and wash use is very less. The daily water consumption will be 25 m 3 /d of which 15 m 3 /d will be used for mud preparation and 10 m 3 /d will be used for domestic purposes including drinking. d. Domestic wastewater The operating personnel in the drilling rigs will operate mostly from nearby ONGC colonies having proper wastewater management systems. However suitable soak pits will be available at the drilling site. e. Solids removal The rock cuttings and fragments of shale, sand and silt associated with the return drilling fluid during well drilling will be separated using Shale Shakers and other solids removal equipment like De-Sander and De-Silter. The recovered mud will be reused while the rejected solids will be collected and discharged into the waste pit. f. Drill cuttings and waste residual muds During drilling operations, approx m 3 per well of wet drill cuttings are expected to be generated from each well depending on the type of formation and depth of drilling. In addition to the cuttings m 3 /day of wastewater is likely to be generated during well drilling. The waste residual muds and drill cuttings which contain clay, sand etc. will be disposed into the waste pit. g. Testing Testing facilities will be available at drilling rig for separation of liquid phase if any and burning of all hydrocarbons during testing. The test flare boom will be located at a distance from the drilling rig. h. Chemical storage The drilling rig will have normal storage facilities for fuel oil, required chemicals and the necessary tubulars and equipment. The storage places will be clearly marked with safe operating facilities and practices. i. Manpower The drilling rig will be operated by approx. 30 persons on the rig at any-time. The manpower will operate in two shifts with continuous operations on the rig. j. Logistics Crew transfers to and from the drilling rig, materials, diesel and chemicals will be through light vehicles, trucks and trailers.