Analyzing Production Data From Unconventional Gas Reservoirs With Linear Flow and Apparent Skin
- Morteza Nobakht (University of Calgary) | Louis Mattar (Fekete Associates)
- Document ID
- Society of Petroleum Engineers
- Journal of Canadian Petroleum Technology
- Publication Date
- January 2012
- Document Type
- Journal Paper
- 52 - 59
- 2012. Society of Petroleum Engineers
- 5.8.2 Shale Gas, 5.6.4 Drillstem/Well Testing
- Linear Flow, Shale Gas, Apparent Skin
- 8 in the last 30 days
- 1,251 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 5.00|
|SPE Non-Member Price:||USD 35.00|
Many horizontal wells with multiple fractures producing from unconventional gas reservoirs have been observed to exhibit linear flow. Often it is the only flow regime, and it can last several years. Classically, this flow regime is characterized by a half slope on type curves when there is no skin effect. However, most of the time, a skin effect is observed in these wells (caused by flow convergence or finite conductivity in the fractures).
The presence of skin changes the shape of data points when plotted on log-log scales, and this can have a huge effect on the interpretation when using type curves. For example, a well with purely linear flow and with skin in a reservoir that is infinite acting may appear like and be interpreted as a finite-acting reservoir simply because of the skin effect.
This paper discusses different methods that can be used to eliminate the misinterpretation caused by the presence of skin when analyzing linear flow by use of type curves. First, it is shown that among all the derivative and integral functions that are currently used, only well-test-style semilog derivative (DER) and pressure integral-derivative are not affected by the skin. However, these two functions have other issues that usually make them unfit for use in production-data analysis. DER is noisy most of the time, and the process of integration often introduces errors at early times that can significantly distort the shape of the pressure integral-derivative. Therefore, an easier method is presented to analyze the production data from shale gas reservoirs with extended periods of linear flow and significant skin. This method uses the square-root-of-time plot to remove the apparent skin effect from the data. Then, the data (excluding skin) are used for type-curve analysis. This simple procedure prevents potentially significant misinterpretation.
|File Size||1014 KB||Number of Pages||8|
Agarwal, R.G., Gardner, D.C., Kleinsteiber, S.W., and Fussell,D.D. 1999. Analyzing Well Production Data Using Combined-Type-Curve andDecline-Curve Analysis Concepts. SPE Res Eval & Eng 2(5): 478-486. SPE-57916-PA. http://dx.doi.org/10.2118/57916-PA.
Anderson, D.M., Nobakht, M., Moghadam, S., and Mattar, L. 2010.Analysis of Production Data from Fractured Shale Gas Wells. Paper SPE 131787presented at the SPE Unconventional Gas Conference, Pittsburgh, Pennsylvania,USA, 23-25 February. http://dx.doi.org/10.2118/131787-MS.
Bello, R.O. 2009. Rate Transient Analysis in Shale GasReservoirs with Transient Linear Behavior. PhD dissertation, Texas A &M University, College Station, Texas (May 2009).
Bello, R.O. and Wattenbarger, R.A. 2009. Modelling and Analysisof Shale Gas Production with a Skin Effect. Paper CIPC 2009-082 presented atthe Canadian International Petroleum Conference, Calgary, 16-18 June. http://dx.doi.org/10.2118/2009-082.
Blasingame, T.A., Johnston, J.L., and Lee, W.J. 1989. Type-Curve AnalysisUsing the Pressure Integral Method. Paper SPE 18799 presented at the SPECalifornia Regional Meeting, Bakersfield, California, USA, 5-7 April. http://dx.doi.org/10.2118/18799-MS.