An Integrated Technique to Optimize the Completions in Low Permeability Gas Reservoirs While Improving Efficiency and Productivity
Authors: Sobernheim D. W. , Aly A. M. , Denoo S. A. , Rowe W. S. , Sturm S. D. , White D. J. 
Published: December 2007

This paper will focus on an applied and integrated real-time technique developed to optimize the completions in low permeability, stacked, lenticular gas sand reservoirs.

This integrated approach involves developing a predictive model based on well logs and pressure transient techniques utilized to calibrate the well logs. The model uses either standard open hole or cased hole log data for calculating reservoir properties, rock mechanical properties, and individual zone productivities. A unique analytical tool was developed to convert continuous log data into discrete layers for input into fracture simulators. A multi-layer simulator is field calibrated to predict individual zone productivity under various stimulation scenarios.

Completions are rapidly designed by multi-disciplinary teams to assure the optimum design based on all available data and knowledge. Data flow is facilitated by an interactive web-based system to allow models to be computed and analysis to be begun within hours of the well reaching total depth. The entire design process must be completed within as few as forty-eight hours to keep pace with extremely aggressive drilling and completion schedules.

The team rigorously pursues systematic learning through comprehensive post appraisals of each completion. Predicted performance is compared to actual well performance on a well-by-well basis for continual improvement of the input models. Production logs and advanced decline curve analysis are strategically employed to provide key data sets. As production logs become available after the hydraulic fracture, new procedures are applied for analyzing the data to quantify estimates of the reservoir effective permeability, effective fracture half-length, and average fracture conductivity within individual productive layers.

This approach involves having a rapid reservoir model at the center of the integrated approach1. The reservoir model is the repository of all the knowledge acquired in the field2. This model is used to investigate and optimize well locations, predict fracture interference problems, and optimize drainage areas. The production data from all the wells are updated in the model on a real-time basis. Drainage patterns, depletion effects, and expected saturation front movements within the reservoir may then be continuously updated and used for forward planning and simulation.

By continuously monitoring and updating the actual production results on the model-based production prediction chart, discrepancies between designed and actual well performance are quickly identified and remedial actions, if necessary, may be efficiently taken. These action steps may include such items as obtaining a production log over the interval to determine what layers are contributing—and which are not, re-checking the completion records to insure that the correct design was pumped, and then applying interventions via coiled tubing and/or re-perforating to correct the situation in the well. The end goal is to quickly get the well on-line, producing to its economic potential.

The result is an integrated technique for a rapid and dramatic turnaround in the optimization of completions in tight gas reservoirs.