Abstract

Extensive data were gathered during the pumping and flowback of a nitrogen foam stimulation treatment on a Devonian Shale gas well in eastern Kentucky. Subsequent analysis of these data revealed that 1) duplicate monitoring equipment, properly calibrated, yielded nearly identical data, 2) the job execution, largely because of extensive quality control, closely followed job design, 3) friction loss in the pumping annulus could be calculated at all stages of the treatment, and 4) both perforation friction loss and the number of holes open could be estimated throughout the job.

As part of the Comprehensive Study Well program sponsored by the Gas Research Institute (GRI). this fracture treatment design, planning, execution, and analysis involved cooperation among planning, execution, and analysis involved cooperation among several GRI contractors, the service company, and the operator. On-site monitoring equipment included densiometers, pressure gauges and transducers, and various types of flowmeters. Two control vans monitored real-time data, and permitted adjustment to one of three tentative pumping schedules based on downhole treating pressures during the prepad stage. Direct measurements led to pressures during the prepad stage. Direct measurements led to real-time calculations of foam quality, foam rate, and downhole proppant concentration. proppant concentration. When the data were analyzed, the wealth of data coupled with the redundancy allowed various calculations to be made with confidence. Direct comparisons between the two sets of monitoring equipment showed near-perfect agreement. Similarly, the actual data matched the design estimates. Recently published results dealing with discharge coefficient change and hole enlargement formed the basis of our analysis of perforation friction.

This analysis has been performed on one other set of data from an offset well and led to similar conclusions. Comparable data is being acquired from other wells and may eventually provide a valuable database for fracture design in the Devonian Shales.

Introduction

Beginning in November 1988, Ashland Exploration, Inc. drilled, completed, and tested the E. J. Evans No. 89 (EJE89) in the Lower and Middle Huron intervals of the Devonian Shale. This well was one of approximately 30 AEI wells completed during the late 1980's in the E. J. Evans lease in Breathitt County, KY, on the edge of the Big Sandy Gas Field. The EJE89 was selected to be Comprehensive Study Well No. 4 (CSW4) in a research program sponsored by the Gas Research Institute (GRI).

The CSW program in the Devonian Shales was a pan of GRJ's continuing research efforts designed to increase the supply of natural gas. This field oriented program had the following main objectives:

  1. to develop a better understanding of the geologic controls on production,

  2. to refine recently developed formation evaluation tools for selecting completion intervals, and

  3. to improve stimulation practices in the Devonian Shales.

The focus of stimulation research in the CSW program was on pumping treatments carrying more sand at higher concentrations, developing an optimal fluid system for the Devonian Shales, and improving quality control.

Breathitt County Shale wells are characterized by relatively thin Shale intervals with 250 to 300 ft gross height from the Cleveland to the bottom of the Lower Huron, and relatively low initial reservoir pressures of 450 to 650 psia. Permeability-thickness products of 1 pressures of 450 to 650 psia. Permeability-thickness products of 1 to 5 md-ft are common, translating to gas flow rates of 15 to 25 Mscf/D, even after stimulation. Historically, the most common type of stimulation for the Shales in this area had been pumping straight nitrogen. Within the past few years, operators began using nitrogen foam carrying low sand concentrations (1 to 2 lb/gal). As with other areas of Devonian Shale production, there appeared to be no particular treatment strategy that outperformed others. In this well, particular treatment strategy that outperformed others. In this well, as with other wells in the CSW program, we recommended pumping a higher sand concentration (6 to 7 lb/gal) nitrogen foam treatment.

The CSW4 was spudded on November 13, 1988 and air-drilled, reaching a total depth of 2805 ft on November 17. Following the logging runs, which included a borehole television survey, 5 1/2-in, 15.5 lb, J-55 casing was cemented in place to a depth of 2791 ft, with the plug at 2760 ft (RKB). Fig. 1 is a well mechanical diagram for the CSW4. On January 6, the operator placed 17 perforations in the Lower and Middle Huron, from 2477 to 2672 ft.

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