Recovery Optimization Through Infill Drilling Concepts, Analysis, and Field Results

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract This paper gives theoretical concepts and some supporting mathematical model and field performance data which demonstrate factors t at performance data which demonstrate factors t at can be involved in recovery increases by drilling. Many of these factors relate to various reservoir heterogeneities and are quantitatively more important in fluid injection projects. Recovery increase by infill drilling projects. Recovery increase by infill drilling of low-permeability waterflood projects can be due to as many as nine different factors with varying degrees of technical difficulty to specifically quantitize. However, based on performance and certain theoretical knowledge performance and certain theoretical knowledge and concepts, reasonable factors involving judgment can be developed as to percent of original oil-in-place recovery increase. Attractive conventional growth economics based on increased ultimate waterflood recovery are indicated for areas of low-permeability, slowly depleting reservoirs with relatively large amounts of oil in place. This is in addition to substantial increases in current rates of production and present worth. Typically, an increase on the order of 4 percent of the original oil in place will be percent of the original oil in place will be gained by infill drilling from 40- to 20-acre spacing. However, this can vary by a factor of two or more depending upon the specific situation. Introduction There is probably no place more than reservoir engineering where a spirit of Hegelian dialecticism applies. That is, there is "truth" and "error." However, in the truth there still exists some error. Consequently, with time a new truth evolves that is purged of some previous imperfections. In the 1940's, Uren, previous imperfections. In the 1940's, Uren, Muskat, and predecessor companies of Exxon, among others, published thinking and results properly decrying misapplications of Cutler's properly decrying misapplications of Cutler's rule. This had been a previous empirical observation which indicated that primary recovery in densely drilled portions of fields was greater and proportional to the square root of well density. It was generally shown that this was due to migration from less densely drilled areas of the same fields rather than an increase in over-all recovery. The tendency since about the 1950's has been to consider increased recovery by infill drilling as negligible or only to consider it where some one factor in a particular reservoir had a dramatic effect upon recovery. This has been partly due to past limitations on ability to realistically describe and simulate actual reservoir heterogeneity and displacement.