Abstract

Historic "sweet spots", areas of well-to-well interference, and infill potential were determined for an 1800 well area of the OZONA (Canyon) field using a new approach that focuses on the age of the wells, their location, and production profiles. At the core of this new approach, termed "moving domain", is a mosaic of automated studies that draw statistical conclusions about well performance, depletion, and undrained acreage. Preliminary infill estimates in one to two weeks are possible and the technique is typically linked to conventional reservoir engineering to improve estimates. When applied to OZONA (Canyon), 1246 infill locations were identified with 636 Bcf of gas reserves.

Introduction

History - The OZONA field, located in Crockett County in Southwest Texas (Figure 1) contains two major producing sands, the Canyon and the Penn. These sands are complex turbidite deposits that are characterized by numerous gas productive members with permeabilities from less than 0.001 mD to over 0.10 mD and are found at depths of 6,000 to 8,000 ft.1 A recent change in field rules will allow drilling to 40 acres spacing in most parts of the field. Initial development began in the early 1960s on 320 acre spacing, with subsequent infill drilling on 160- and 80 acre spacing. Typical completions require fracture treatments using water based fluids containing 50 to 250 klbs of 20/40 sand to achieve economic production rates. Ultimate gas recoveries range from 200 MMCF to over 2000 MMCF and can vary significantly from well to well. Historically, many wells with multiple pay zones were fracture treated simultaneously, while other wells were fracture treated in isolated stages.

Problem - Quantifying the infill potential in the OZONA (Canyon) field is difficult for several reasons: the layered and low permeability nature of the reservoir, the hydraulic fracturing of wells, the variation in well spacing, and the local and regional variations in rock quality. These complicating factors often cloud the extent of depletion, benefits of improved completion and operation techniques, and make the quantification of infill potential rather difficult. Because of these complexities and the fact that our study area contained over 1000 wells, the time and cost requirements of a conventional reservoir engineering study were unacceptable. Instead we applied a new technique that was found to be useful in a large tight gas field in East Texas.2

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