Testing Tight Gas and Unconventional Formations and Determination of Closure Pressure
- Mohamed Y. Soliman (Texas Tech University) | Talal D. Gamadi (Texas Tech U.)
- Document ID
- Society of Petroleum Engineers
- SPE/EAGE European Unconventional Resources Conference and Exhibition, 20-22 March, Vienna, Austria
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.6.3 Deterministic Methods, 3 Production and Well Operations, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.1.2 Separation and Treating, 1.6 Drilling Operations, 5.8.1 Tight Gas, 5.8.4 Shale Oil, 5.8.2 Shale Gas
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Experience indicates that applying the conventional testing techniques such as drawdown-buildup tests to unconventional reservoir may lead to non-unique answers. Diagnostic testing approach is now more commonly used in tight gas formations and unconventional reservoirs. Testing unconventional reservoirs, particularly hydrocarbon-bearing shale formations, presents considerable challenges. In addition determination of the fracture closure pressure is sometime elusive. This paper reviews those challenges faced in analysis of testing of tight gas and unconventional reservoirs both liquid and gas.
Conventional testing and analysis methods, although applicable, are often impractical because of excessive test duration. Diagnostic fracture injection test (DFIT) has become the preferred option for unconventional formations. Several methods may be used for interpreting DFIT data. We examine those methods in detail and explore their relative strengths while interpreting field data. We also show ways to determine the fracture closure pressure under various reservoir and fracture
Unlocking the potential of unconventional gas reservoirs is changing the balance and future of the energy industry. Unconventional gas reservoirs may be tight gas, coal-bed methane (CBM), or shale reservoirs. Unconventional shale oil reservoirs, such as the Bakken, present another dimension to the exploitation challenge. Economically producing any of these types of reservoirs requires the creation of multiple transverse fractures in a long horizontal well. Fracturing horizontal wells necessitates learning of rock mechanics, change of stresses around the created fractures, and fluid flow. Therefore, testing becomes a critical part of assessing completion design and the initial-reservoir pressure, thereafter leading to any reservoir engineering calculations. However, testing unconventional formations presents special challenges that needs addressing.
Analysis of diagnostic tests would indicate whether and how further completion and exploitation of the reservoir should proceed. Analysis of data usually means the determination of formation permeability and initial reservoir pressure. In this paper we also show a more deterministic way of also determination of closure pressure. In addition we show a technique that compliments the G function analysis for determination of the deviation from the ideal behavior of fracture closure. We will show that this technique is applied best to very low permeability formation and unconventional reservoirs.
Shale formations differ from conventional reservoirs in several aspects. Shale formations are usually naturally fractured with the matrix permeability in the nano-darcy. In addition the matrix usually has some organic carbon that may have some adsorbed gas. This total organic carbon (TOC) may be as high as 10% of the matrix. These differences indicate that a conventional test would have to be un-realistically long to accommodate the ultra-tight nature of the shale formations. It will
also mean that both free and adsorbed gas co-exist which could complicate the testing procedure.
The nature of shale formation represents a challenging task to analysts. Tests will have to be especially designed to allow the analysts to determine the sought after reservoir properties. New analysis techniques or new testing procedures will have to be developed to produce meaningful reservoir results.
Economic production of shale formation is attained by drilling a horizontal and creating multiple transverse fractures. Because of all the factors discussed earlier, pre-fracturing tests are not usually run. Post fracturing testing is the main vehicle to getting reservoir information. DFIT and MiniFrac tests performed before running the main fracturing treatments are the ideal testing methods.
|File Size||3 MB||Number of Pages||6|