Production analysis is commonly performed in tight gas reservoirs as this analytical technique can be used to quantify reservoir flow capacity, gas in-place, and reservoir geometry (both area and aspect ratio). The results have been used to estimate the effective drainage area, infer completion efficiency and evaluate infill drilling potential for tight gas reservoirs. The question addressed in this lecture is, “When performing production analysis, can complex reservoir geometries and completion practices cause linear flow, limited effective fracture half lengths and limited drainage areas to be predicted”. The short answer is "yes". Complex reservoir geometries and post production completion techniques do influence the results obtained from transient production decline analysis. This talk will demonstrate the effects of stress dependent permeability, radial composit reservoirs and multi-layered reservoirs on the results obtained from production analysis. The completion issues addressed will include hydraulic fracture cleanup, fracture conductivity reduction and liquid loading. Laboratory studies and field examples will be presented that demonstrate the effect of liquid loading on well performance and the resulting production increase after the liquid loading was eliminated. The ability to analyze the effects clearly helped us to correctly evaluate well performance and implement steps to improve future well performance. For tight gas reservoirs it is common to observe limited drainage areas and linear flow geometries. In some cases these results are inconsistent with the expected geological structural and depositional character of the reservoir. Complex reservoir geometries and flow conditions can contribute to this phenomenon. The one idea I would like members to take away from this lecture is that "Production analysis is a powerful analytical technique that can shed light on completion and reservoir performance. However, many common events that occur in wells can compromise the accuracy of the results and when properly adressed can result in improved well perfromance."
Stuart Cox is a Senior Technical Consultant with Marathon's Technology Services organization in Houston, Texas. He has 23 years of experience focused on operations and reservoir engineering. Since 1990 Stuart’s primary focus has been production optimization of tight gas reservoirs. Over the past twelve months Stuart has made eight technical presentations outside the company at industry meetings on the topics of production analysis and well optomization. He was also a guest lecturer at Tulsa University and New Mexico Tech this past year. Stuart is an inhouse instructor for Marathon Oil Company for pressure transient analysis and production analysis. He graduated from the University of Tulsa with a B.S. degree in Petroleum Engineering in 1984 and is a registered professional engineer in Alaska and Oklahoma. Stuart has authored twelve papers published by SPE on this topic.
Stuart was an SPE Distinguished Lecturer in 2009-10.