Abstract

Horizontal well activity has increased in the United States and has proven successful in numerous applications. This paper presents the steps undertaken to optimize the application of fractured horizontal technology in a shallow, low pressure gas reservoir. An application of limited entry technology to create a longitudinal propped fracture through a predrilled liner was developed. Available data for fracture direction, acoustic logs, and mechanical property measurements were used in designing the fracture treatment. Tagging the pad, sand, and resin coated sand with isotopes was used to verify the fracture extended along the entire horizontal lateral.

Introduction

To date, vertical wells in the Guymon-Hugoton have proven inexpensive and effective at draining the gas reserves in this shallow, low pressure, multi layer field. All vertical wells in the Guymon-Hugoton are propped fractured, and most field diagnostics indicated that bigger treatments did not produce longer fractures due to a lack of height containment. The challenge was finding a technology to increase not only the production rate, but also the efficiency of capital measured on a $/mcfpd basis. Horizontal drilling was selected as today's best technical solution to this economic challenge.

Preliminary studies concluded multiple horizontal laterals were not economically viable. Therefore, for these studies, all well configurations assume a single horizontal lateral with a fracture stimulation treatment to communicate the multiple productive layers with the horizontal wellbore. Concurrent studies were undertaken to optimize each piece of the drilling process from location selection to well design including the length of the horizontal lateral and the completion methodology. The result was a well with a significant increase in productivity index at a cost per mcfpd 30% lower than a new vertical well.

Geology/Reservoir Description

The Hugoton Field stretches 175 miles from southwest Kansas through the Oklahoma Panhandle and into the Texas Panhandle (see Figure 1). It is the largest gas field in the lower 48 states representing a significant portion of the domestic gas production (1.4 BCF/D) and reserve base.

Our focus was the Guymon-Hugoton Field, lying in the Oklahoma Panhandle. Gas production is from the shallow (2500-2900 ft), low pressure (130 psia), multi-layered, no crossflow gas reservoir in the Lower Permian Chase Group. The layers within the Chase Group, shown in Figure 2, are carbonate dominated and separated by siltstone intervals. The productive layers within the Guymon-Hugoton Field are the Herington, Upper Krider, Lower Krider, Winfield and Towanda. The Fort Riley and Wreford intervals, which are productive in the Kansas Hugoton Field, are water bearing in the Guymon-Hugoton Field.

The average reservoir properties for the target area are shown in Table 1. These properties were calculated from a Kansas Hugoton well three miles north of the proposed location. The lithology and depths were taken from a nearby vertical well producing from a deeper horizon.

Well Drilling and Completion Design

Location Selection. Drilling began in the Guymon-Hugoton Field in the 1920's with full development by the 1950's. The wells are spaced, on average, at a density of one per 640 acres corresponding to a section. Since the field is fully developed and infill wells are not allowed by the field production rules, a new horizontal well would be a replacement for the existing vertical well.

The location was selected using a three phase process.

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