An Effective Technique of Estimating Drainage Shape, Magnitude and Orientation in a Low-Permeability Gas Sand

Abstract

This study presents a methodology to determine the optimal infill location for the Mesaverde Field in the San Juan Basin, New Mexico. Evaluation techniques include:Log-derived cumulative distributions to develop producing interval limits,Seismic analysis to identify fractures,Type-curve analysis to generate reservoir properties,Production decline analysis for establishing inter-well relationships,Geostatistical modeling to distribute reservoir characteristics, andFlow simulation for verification and formation contribution. The result of incorporating these evaluation methods is a map that provides limits to the drainage area. Specific information obtained is degree of anisotropy, aspect ratio, and the magnitude and orientation of the permeability. In the study area, the dominant fracture orientation was N30°E as indicated by seismic curvature analysis and confirmed with production decline analysis. Type-curve analysis resulted in an average well permeability from 0.10 md to 7.75 md. It was demonstrated that a minimum permeability ratio (kmax/kmin) 13.7:1 was sufficient to match the interfering production response exhibited between wells. Limited infill drilling was identified on the drainage maps, as the existing wells exhibit an average drainage area of approximately 160 acres. Potential recovery was estimated to be 800 MMscf per well for the selected locations with the best chance for success. A common problem in infill drilling projects is to decide to target prolific areas or low reservoir quality areas in the Mesaverde Group. This study area consists of high equivalent permeability as a function of naturally occurring fracture networks, when compared to the rest of the basin. The likelihood of widespread drainage to occur is high. Therefore, the potential for infill drilling may be limited. This work demonstrated that although limited potential, exists, proper evaluation methods established in this work might be useful to identify the best location. Introduction A conceptual study by Harstad (1998)1 investigated the effects of permeability anisotropy and well alignment on infill well placement. More recently, Al-Hadrami and Teufel2 investigated the effects of permeability anisotropy and heterogeneity on infill drilling in the Mesaverde. This study continues from these previous works by demonstrating a method to determine drainage areas of existing wells, and the consequence on infill well potential in a study area which is extremely natural fractured; thus providing an excellent test case for the method. The proposed method of analysis for low-permeability, naturally fractured, gas producing formations relies on minimal data for analysis. Required data for the methodology presented here includes gamma ray and bulk density well logs, completion and production history data, and a few basic reservoir properties, all of which are typically the minimal acquired data for any given producing hydrocarbon deposit. The Mesaverde Group is a low-permeability gas reservoir located in the San Juan Basin, northwestern New Mexico. It is comprised of three formations. From shallowest to deepest, they are, Cliff House Sandstone, Menefee Formation, and Point Lookout Sandstone. The Cliff House and Point Lookout are massive shoreline sand deposits that span most of the basin. The Menefee consists of discontinuous channel sands that result from a estuarine, deltaic and fluvial geologic environment (Harstad, 1998). The dominant producing formations vary throughout the basin due to thickness differences and natural fracture dependent permeability, and since the production is commingled, the true contributions from each formation are unknown.

Anisotropy Gas Reservoir Drainage Radius and Quantitative Well Interference Study

“…Furthermore, more parameters can be obtained. Blasingame and Lee [1] use the gas seepage formula of pseudo time function and it can be used for the analysis of general changes in production or unsteady pressure drop in the process of gas well production. The material balance equation can be amended as follows for the gas well by using the pseudo pressure and pseudo time functions, Eq.…”