This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 91755, "Fast Method Finds Infill-Drilling Potentials in Mature Tight Reservoirs," by L. Guan, SPE, Texas A&M U., and Y. Du, SPE, New Mexico Inst. of Mining and Technology, prepared for the 2004 SPE International Petroleum Conference in Mexico, Puebla, Mexico, 8-9 November.

Infill drilling plays an important role in improving oil or gas recovery in tight hydrocarbon reservoirs. However, quantifying the infill-drilling potential in these fields often is difficult because of variability in rock quality, well spacing, well-completion practices, and the large number of wells involved. An alternative approach to conduct de-tailed reservoir studies for infill drilling has been developed.

Introduction

One key to ensuring an abundant, economical, and environmentally friendly supply of natural gas is developing the resources in unconventional, low-permeability, tight reservoirs. Although the average production rate of gas wells from these reservoirs is low, they play an important role in the petroleum industry. Infill drilling these reservoirs after initial development (primary and/or secondary) plays an important role in improving the oil and gas recovery. Generally, the effects of reservoir heterogeneity and lack of layer continuity can be reduced with well spacing. Reduced well spacing can enhance the well connectivity.

With the increasing demand for energy and favorable oil and gas prices, more fields are undergoing infill drilling. Advances in reservoir management provide a much clearer picture of hydrocarbon distribution in the reservoirs, which helps engineers plan highly effective well profiles. Advanced imaging technologies allow operators to optimize well placement for infill drilling. It is not uncommon for a company to have many infill candidates to choose from in the tight-reservoir fields. The conventional way to determine infill-drilling potential in a gas basin is to conduct a complete reservoir evaluation involving geological, geophysical, and reservoir analyses and interpretations. As an alternative approach to conducting detailed studies, various empirical or statistical analyses have been used to model variable well performance. The objectives of this work were to study the accuracy of a “fast method” for selecting infill candidate wells in low-permeability gas reservoirs and to provide application guidelines.

Method

This fast method is an extension of the moving-window method. It consists of multiple local analyses, each in an areal window centered on an existing well. However, a more rigorous, model-based analysis is used in each moving domain. The model is based on a combination of the material-balance equation and the equation for pseudosteady-state flow, simplified by assuming that many properties are constant within an individual moving domain. The result is a linear-regression equation that is applied within each window.

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