Wireline Pressure Measurements Improve Reservoir Characterization in Tight Gas Formation

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 109565, "A Case Study: Using Wireline Pressure Measurements To Improve Reservoir Characterization in Tight-Formation Gas¡ªWamsutter Field, Wyoming," by R.A. Schrooten, SPE, BP America; E.C. Boratko, SPE, H. Singh, SPE, and D.L. Hallford, SPE, Schlumberger; and J. McKay, BP America, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11-14 November. Improving recovery in tight gas reservoirs typically requires infill-drilling programs. Characterization of reservoir-pressure depletion and sand-body continuity is fundamental to determining the economic viability of these projects. In tight gas reservoirs, new wireline tools that use precise pretest mechanisms can achieve the required data-acquisition objectives. However, wellbore conditions and data-acquisition procedures can greatly influence the quality and limits of data application. Introduction The Wamsutter field is a large, continuous tight-formation gas accumulation in the Washakie and Red Desert basins of the Greater Green River basin in southwest Wyoming. Discovered in the 1950s, it encompasses 1,700 sq miles and is one of the largest tight gas resources in North America. The field area has produced 2 Tcf from more than 2,000 wells since discovery in the late 1950s. The primary productive interval is the Almond formation of the Mesaverde group, comprising shallow marine sandstones deposited along the western margin of the Cretaceous seaway. Improving recovery in tight gas reservoirs leads to tight well spacing, driven by reservoir connectivity, permeability, well costs, and gas prices. These fields typically go through multiple rounds of downspacing on the basis of development pace, well-performance maturation, increased reservoir-characterization information, and technology advancements. This process can lead to less-than-optimal spacing and completions. An elusive challenge with tight-formation spacing studies has been to gather fit-for-purpose pressure data in these reservoirs. A typical Wamsutter well will encounter a 500-ft gross (100-ft net) interval in the Almond, comprising 10 to 20 sands each averaging less than 10 ft in thickness. The result is a high level of heterogeneity. The historic inability to adequately or accurately sample individual-sand pressures throughout the productive interval while infill-developing mature producing areas has relegated historic drainage and recovery characterizations to overly simplistic and overly homogeneous tank-type material-balance solutions. The lack of dynamic layer-by-layer depletion detail can lead to erroneous modeling or poorly constrained recovery predictions and equally flawed claims for well-spacing requirements.