Analysis of Completion and Stimulation Techniques in a South Texas Field Utilizing Comprehensive Reservoir Evaluation

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractMost of the major unconventional gas plays in the U.S. have multiple productive intervals. Wells are completed with multiple fracture treatments, and are produced commingled. This paper describes a new fully-coupled reservoir/wellbore single-well analytical simulator * for multilayer unconventional gas reservoirs that automatically history matches production and production log data simultaneously.The layers in the simulator are independent, with different temperatures, pressures, completion types, and reservoir geometries. The simulator rigorously accounts for transient and boundary-dominated flow in each layer and pressure drop in the wellbore, including pressure drop between adjacent layers and pressure drop from the reservoir to the surface.By history matching data from multiple production logs as well as surface production data, the simulator provides accurate estimates of individual layer properties such as permeability, fracture length, and drainage area.The simulator may be used for reservoir and fracture treatment evaluation, restimulation candidate selection, fracture design optimization, and performance forecasting in multilayer unconventional gas plays.

Estimating Layer Properties for Wells in Multilayer Low-Permeability Gas Reservoirs by Automatic History-Matching Production and Production Log Data

Spivey

2006

Fracturing Previously Bypassed Highly Laminated Tight Gas Sands: A Production Optimization Case Study in South Texas

Fairhurst

Semmelbeck²,

Reynolds

et al. 2007

Highly laminated tight gas sand sequences remain prolific targets worldwide and have often been bypassed using standard petrophysical analysis and simple porosity cutoff technique. The problem becomes more acute in marginal tight gas reservoirs. The high cost of hydraulic fracturing increases the need for an effective and useable petrophysical model for an accurate productivity indication of the target interval. The pressure to avoid non-economical completions continues to leave hydrocarbons bypassed. Using recent advances in logging technology and production optimization modeling, the thinly laminated gas bearing permeable sands can be discerned from clay dispersed in silt and sand. A true net height can now be obtained. Through production optimization modeling, it is possible to assess the economic viability of completing and stimulating highly laminated interval. In this paper, we will show a case study from a South Texas tight gas sand field. Several wells were evaluated using micro-resistivity imaging. From this an enhanced high-resolution petrophysical analysis was created. This image-enhanced evaluation of reservoir properties was combined with production modeling. The production performance was simulated for each interval and used for recommendations on completion strategies. Additional pay intervals, normally bypassed, were perforated and hydraulically stimulated. We compared production data from offset wells that used standard petrophysical analysis to the results of the newer wells with the high-resolution analysis. The results indicated that actual field production increased and paid out the increased fracture stimulation cost. Production logs acquired across entire intervals confirmed that portions of the field produced from horizons that were previously bypassed. This process is useful for any highly laminated tight gas sand sequence and is of widespread applicability. Previously bypassed intervals can now be assessed and completed effectively and economically. This process will further add to the reserve base of tight gas.

Production Data Analysis for Commingled Multilayer Gas Reservoirs—Graphical Aides for Flow Regime Identification and History Matching

Spivey

2007

Most of the major unconventional gas plays in the U.S. have multiple productive intervals. Wells are completed with multiple fracture treatments, and are produced commingled. An earlier paper1 described a single-well, multilayer, analytical reservoir simulator* for estimating individual layer properties in multilayer unconventional gas reservoirs by automatic history matching production and spinner survey data simultaneously. The present paper describes several interactive graphical aides that greatly facilitate the history matching process when used in conjunction with the analytical, multilayer reservoir simulator. These graphical tools include an allocation graph and layer and cumulative production log graphs. These graphs allow the engineer to quickly review the quality of the match at any point during the history matching process. Use of these graphical tools has improved the history matching workflow to the point that a complete history match of a well with 20 frac stages, two years of daily production, and three spinner surveys can be performed in as little as four to six hours, from construction of the initial data set through completion of the final match. Introduction Wells in low permeability and other unconventional gas reservoirs are often completed by commingling production from multiple intervals, as shown in Fig. 1. In many cases, intervals are too far apart vertically to be produced by a single hydraulic fracture, so multiple fracture treatments must be used. Estimating reservoir and fracture properties for individual layers in such reservoirs is crucial to evaluating fracture treatment effectiveness, optimizing future stimulation treatments, and forecasting future performance. Fig. 1-Gas well in a multilayer unconventional gas reservoir with commingled production. In single-layer unconventional gas reservoirs, production data analysis has been one of the most useful tools for estimation of reservoir and fracture properties. Single-layer production data analysis methods include type curve matching using constant pressure type curves2–5, type curve matching using constant rate type curves6–9, and automatic history matching using an single-layer analytical reservoir simulator10–13. To estimate individual layer properties for wells with commingled completions, production log (spinner survey) data must be incorporated into the production data analysis workflow to separate the contributions of the individual layers. One method that has been proposed is to allocate production to individual layers by interpolation using the spinner survey data, then analyze the resulting reconstructed individual layer rate histories using single-layer methods14–16. Unfortunately, if there is a strong contrast in layer properties, the allocation method will not accurately reproduce the individual layer flow rates, thus leading to erroneous estimates of layer properties1.