Extending Well Productive Life with Acid Re-fracturing in a High Pressure/High Temperature Tight Gas/Condensate Carbonate Reservoir
- Mir Md. Rezaul Kabir (Field Development Consultancy) | Qasem M. Dashti (Kuwait Oil Company) | Jai Ram Singh (Kuwait Oil Company) | San Prasad Pradhan (Kuwait Oil Company) | Ikhsan Nugraha (Schlumberger Oilfield Eastern Limited) | Hamed Al Ghadhban (Schlumberger Oilfield Eastern Limited) | Liu Jin Hua
- Document ID
- Society of Petroleum Engineers
- SPE Middle East Unconventional Gas Conference and Exhibition, 31 January-2 February, Muscat, Oman
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 1.10 Drilling Equipment, 2.2.2 Perforating, 4.1.2 Separation and Treating, 2.5.1 Fracture design and containment, 3.2.4 Acidising, 5.3.4 Integration of geomechanics in models, 1.8 Formation Damage, 1.6.9 Coring, Fishing, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.8.1 Tight Gas, 3 Production and Well Operations, 5.6.9 Production Forecasting, 4.3.4 Scale, 5.2.1 Phase Behavior and PVT Measurements, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.2.3 Rock properties, 5.3.2 Multiphase Flow, 5.8.7 Carbonate Reservoir
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One of the most common strategies to effectively produce from tight gas carbonate reservoir is by completing the wells with acid fracturing technique, where the etched fracture half length alters the flow pattern from formation in to the wellbore with its high conductive flow path.
The treatment success, apart from operational aspects, is also measured by addressing the issue of fractured geometry created, zonal coverage achieved and the actual well potential based on its petro-physical and rock mechanical properties and relate this to well's production behavior. In the high pressure/high temperature tight rock formation with minimum number of natural fractures, it is very common to observe immediate production gain following an acid fracturing treatment.
The well in discussion was acid fractured 3 years earlier with almost 90% of cumulative production occurred during the last one year. It was observed that it is declining faster than expected. Review of the well performance led to two main possible causes, i.e. reservoir pressure decline and reduction in fracture length/conductivity. Acid re-fracturing strategy was considered and decided to restore the well's productivity by further extending the fracture half length by enhancing the fracture conductivity.
The results showed that Productivity index (PI) increased by 2.5 folds during the post treatment production test. However, after 3 months of continuous production, the PI declined down to 1.2 folds despite the pressure build up performed indicated fracture conductive behavior. This paper discussed key lessons learned to further improve the outcome by integrating production analysis, reservoir quality evaluation as well as stabilized production expectation with stimulation approach during candidate evaluation process.
The Jurassic formation of North Kuwait consists of several major fields such as Sabriyah, Raudathain, Umm Niqqa, Bahra & Dhabi. Middle Marrat within Jurassic formation of these fields is one of most important carbonate reservoir contributing to the total gas production. Typical depth of Middle Marrat is ~14,000 ft where the reservoir pressure is in the range of 10,000 - 12,000 psi with average bottom hole static temperature of ~275 deg F.
Middle Marrat formation is mostly dominated by limestone (calcite > 90%) with minor dolomitization. Only trace of clay and silt are typically found. High heterogenety both laterally and vertically has also been reported. However, the core permeability is matching with log permeability, where the high permeability value obtained from the core could be due to induced fracture as well. On the other hand pressure transient analyses done on some wells are also showing dual porosity behavior with low matrix permeability. However, in general the absolute matrix permeability is generally less than 1 md. It is believed that the production mechanism is contributed through a combination of matrix and natural fracture permeability.
Acid Re-fracturing Revisit
In places where acid fracturing is a common practice, there are several questions that usually arise, i.e. when is the best time to do re-fracturing, what is the justification to repeat the treatment, and if there is, what needs to be done different in the subsequent treatment. The decision making process usually rely on the post frac production behavior compared with the pre- fractured condition.
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