The paper was presented at the SPE/DOE Unconventional Gas Recovery Symposium of the Society of Petroleum Engineers held in Pittsburgh, PA. May 16–18, 1982. The material is subject to correction PA. May 16–18, 1982. The material is subject to correction by the author. Permission to copy is restricted to an abstract of not more than 300 words Write: 6200 N. Central Expwy., Dallas, TX 75206.

Abstract

A project jointly funded by Mountain Fuel Supply Company and the U.S. Department of Energy is being conducted to show the commercial potential of recovering methane gas from deep coal seams in the Book Cliffs coal field in Central Utah. Recovery technologies are being defined and economic analyses of methane recovery are being made. Three vertical wells have been drilled to depths ranging between 3,000 and 4,110 feet. Desorption measurements on core samples indicate gas contents up to 440 cu ft/ton. All three wells have been subjected to hydraulic stimulation treatments but with drastically different results. One well has demonstrated gas production of 20 to 30 mcfd from a 13-foot coalbed. A second well was extremely "tight" and very little production has been achieved to date. The third well has not been put on continuous production, but gas production rates of 120 mcfd averaged production, but gas production rates of 120 mcfd averaged over a short testing period were measured.

Introduction

Since January 1979, Mountain Fuel Supply Company, with joint funding from the Morgantown Energy Technology Center (METC/DOE), has been conducting a project to demonstrate the economic feasibility of recovering methane from deep unmineable coalbeds in Utah. Three wells have been drilled under this project. All three are located in Carbon County, Utah in a prominent coal field known as the Book Cliffs. Data previously collected by the Bureau of Mines and the Utah Geological and Mineral Survey showed that the coals in this field contain relatively high volumes of methane gas. The well sites chosen for this project were selected based on this gas content data, coal depth, accessibility, and proximity to one of Mountain Fuel's major transmission pipelines.

DRILLING AND COMPLETION

Three project wells have been drilled. The first two were drilled late in 1979 while the third well was drilled late in 1981. The first two wells are spaced about 1,800 feet apart in the Whitmore Park area approximately 23 miles northeast of Price, Park area approximately 23 miles northeast of Price, Utah. The wells were drilled to depths of 3,000 feet and 3,177 feet. Coalbeds were encountered between 2,681 and 3,112 feet. The third well was drilled about 12 miles north of Price to a total depth of 4,110 feet. Coals were encountered between 3,494 feet and 4,019 feet. The wells intersected coal seams ranging in total thickness from 33 feet to a maximum of 46 feet. Only the larger and more attractive coalbeds in each well were selected for completion, but additional coalbeds may be completed in the future. A 6-foot Sunnyside coalbed was completed in Well No. 1. This was a cased-hole completion with conventional perforations into the coalbed. Well No. 2 was completed open hole across a 13-foot Gilson coalbed. Well No. 3 was completed into ten zones each containing coal seams ranging from 2 to 6 feet thick. Conventional perforations were made for 9 zones while the tenth was completed using a selective completion tool.

It became apparent as the work progressed on each of the first two wells that the proximity of a coalbed to one of many water aquifers present in the area presented development problems. Since the third well was drilled two years after the first two wells, the insight gained from the earlier drilling was applied in selecting the coalbeds for completion in the final well.

To maximize the methane recovery from the third well it was desirous to produce from as much coal as possible without running too high a risk of opening a possible without running too high a risk of opening a coalbed that might also open an adjacent water aquifer. The quality of the coal in each seam was estimated from a density log and a combination of sonic log, gamma ray, compensated neutron formation density, dual induction-SFL, dual laterlog, and Saraband logs were used to identify the formations above and below each coalbed. Particular attention was paid to sandstones with high porosity which could produce substantial water flows. Table 1 shows a produce substantial water flows. Table 1 shows a summary of the coalbeds and surrounding formation analysis.

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