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Unconventional and Complex Reservoirs
Pre-fracture Treatment of Coal Seams for Fracture Conductivity Enhancement in Hydro Fracturing of CBM Wells and Coal Fines Mitigation in Multilateral CBM Wells through Wettability Alteration of Coal Fines - A Laboratory Study
Kumar, Ajay (ONGC) | Roy, D. C. (ONGC Ltd, India) | Yadav, N.. (ONGC Ltd, India) | Rao, Y. R. (ONGC Ltd, India) | Singhal, C. P. (ONGC Ltd, India) | Kumar, Ajit (ONGC Ltd, India)
Abstract India has sixth largest coal reserves in the world and estimated to be at 206 billion tons and it ranks 10th in CBM resources having 4.6 TCM methane gas covers 20,000 km2 of area. The CBM reservoirs is multilayered, heterogamous, naturally fractured (cleats) and having fine micro pores. Bulk porosity of the coal is very small (<5%), the initial gas saturation is very low (<10%) and most of the gas in coal (>90%) is adsorbed in the micro pores of coal matrix and under saturated condition. Rapid dewatering is needed for reduction the reservoir pressures below critical pressure for desorption of gas from coal bed. Therefore, conventional / horizontal well with fracturing, multilateral well to cover many zones in CBM is being opted for economic exploitation. More than 60 no of conventional and horizontal/multilateral wells are drilled so far and many of them are completed with hydro-fracturing. As coal is a weak substance and small pressure can cause the coal to fail and generate fines, hence enormous coal fines are normally produced during production (in case of high draw-down) and during hydro fracturing of coal seams. In some fracturing job, fines generation & migration reduces the fracture length and conductivity lead to reduced dewatering. Similarly, in multilateral well of CBM, coal fines are accumulated at the heel of the well in case of high draw drawdown and creating the restriction in dewatering and gas production. In view of the above, innovative pre-fracture treatment technique with innovative formulation (Mixture Nonylphenoxy polythyleneoxide and Nonylphenoxy polythyleneoxide in the ratio of 1:2 with 0.5 % biopolymer) is developed & successfully tested in laboratory to change the wettability of the coal fine by making it hydrophobic to hydrophilic. Coal fines can easily come out with water based fluid during pre-treatment, hydro-fracturing and multilateral wellbore cleaning.
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.34)
- Well Drilling > Drilling Operations > Directional drilling (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Coal seam gas (1.00)
Abstract Realtime formation evaluation is critical not only for various geomechanical applications but also for quick drilling decision making in both exploration and development scenarios. The study focuses on a horizontal development well in a carbonate field which has a thin oil column overlain by a large gas cap. Large exposure multi-lateral development wells are used to improve drainage of the oil column by reducing the tendency for gas coning. The real time formation evaluation proved formation fluid in the landing section as gas, and as a result a quick decision was made to change the well trajectory. The well was drilled 20m down in TVD as a pilot well to perform down hole fluid profiling using the Modular Formation Dynamics Tester (MDT), however, MDT could not be carried out due to heavy mud losses and the well was plugged. Finally, it was decided to sidetrack the well. MDT with Live Fluid Analyzer (LFA) and Compositional Fluid Analyzer (CFA) was deployed to perform downhole fluid profiling in the side tracked well to identify the hydrocarbon type and composition at 3 stations. With the help of inclinometry information well trajectory and probe orientation were monitored so that sampling points were selected with probe on the high side of hole and outside of sumps if present. Fluid scanning stations using CFA/LFA clearly indicated the fluid type as gas. Fluorescence was monitored in real time to ensure that gas samples were collected above dew point. Samples collected at 3 depths were examined at surface and to confirm the CFA result. The CFA provided the C1, C2-C5, C6+ weight fractions, GOR and apparent hydrocarbon density in real-time. The fluid analysis recorded by the CFA matched well with the known gas composition and fluid density after corrections for mud filtrate were applied. This paper shows the importance of LWD in terms of quick real-time decision making over wire line logs which are recorded after the well is drilled up to target depth. The downhole fluid profiling in sidetracked well helped in taking quick decision as not to drill further.