Detection of Hydraulic Fracture Orientation And Dimensions in Cased Wells

Abstract

A promising technique for recovering gas reserves combines large hydraulic fractures with multiple-zone completions in a single well. An accurate knowledge of the dimensions, orientation, and spatial characteristics of the fractures is needed. This paper reports research on the use of large hydraulic fractures and multiple completions conducted in conjunction with projects for detecting and measuring fracture dimensions and orientation. projects for detecting and measuring fracture dimensions and orientation. Introduction The need for the nation to expand its natural gas reserves has become increasingly apparent to both the industry and the layman in recent years. Considerable gas in place exists in several Rocky Mountain sedimentary basins in tight reservoirs that are not now included in the nation's reserves because of a lack of means to economically recover this gas. Fig. 1 shows the location of some of the more predominant sedimentary basins in the mountain area of the west. A recent national study estimates that the nation's recoverable natural-gas reserves could be doubled if economic means could be developed to recover about half the gas from the tight sandstones in the Green River, Uintah, and Piceance Basins alone. Many of these potential reserves are contained in large vertical intervals up to 4,000 ft thick. One of the promising techniques for recovering this gas combines promising techniques for recovering this gas combines the use of large hydraulic fractures and multiple-zone completions in a single well. For example, economic completion of a well in the northern Green River Basin may require hydraulic fracturing of more than 100 individual pay sands in a single well in up to 10 completion stages. One proposal would require 8 million gal of fracturing fluid and 15 million lb of sand proppant for a single well. Propped fractures would extend about 1/2-mile from the wellbore. Economic development of such a gas reservoir using these fracturing techniques will require an accurate knowledge of the dimensions, orientation, and spatial characteristics of the fractures. Well spacing must be correlated with fracture orientation to minimize interference of drainage patterns and, thus, maximize economic-recovery potential. Fracture dimensions and spatial characteristics are the key to understanding reservoir exposure and production characteristics. The completion of gas wells in these tight sands will require casing to insure well integrity and to minimize production problems. However, the use of casing limits production problems. However, the use of casing limits the usefulness of the standard tools for defining fracture properties. Casing prevents the use of impression properties. Casing prevents the use of impression packers to determine fracture height and orientation and packers to determine fracture height and orientation and severely limits sonic and electromagnetic techniques. Temperature and radioactivity tools do work at only slightly reduced efficiencies. Even in uncased wells, the plane and direction of a hydraulic fracture can be directly observed only at the wellbore with standard techniques. What is needed is a means to measure the dimensions and orientation of the induced fracture over its entire area. El Paso Natural Gas Co. is presently conducting research in the use of large hydraulic fractures and multiple completions in the Pinedale Unit in the northern Green River Basin. In conjunction with this effort, research projects implemented by El Paso, Sandia Laboratories, and Globe Universal Sciences have the goal of detecting and measuring fracture dimensions and orientation. Exploratory experiments also have been performed in the San Juan Basin in New Mexico. These performed in the San Juan Basin in New Mexico. These sites are shown in Fig. 1. This paper is a progress report on these fracture-detection efforts. P. 1116