Abstract

This paper summarizes the results of a larger study assessing the economic potential of extensive infill drilling in the San Andres/Grayburg, South Central Basin Platform Play. The study provides estimates of Play. The study provides estimates of economically recoverable crude oil and associated gas from infill drilling in 19 West Texas carbonate fields contained in the play. A detailed geologic and engineering analysis was conducted on a specific 640-acre section of the Dune Field (Section 15), which was considered to be representative of the fields in the play and was used for evaluating the potential infill recovery in the analyzed potential infill recovery in the analyzed reservoirs. Estimates of recoverable oil and associated gas were contrasted for reductions in well spacing from 80 acres to 10 acres per well, using a uniform or "blanket" infill drilling program compared to a geologically targeted, "strategic" infill drilling program.

The results indicate that, due to reservoir heterogeneity, significant volumes of oil and gas are economically recoverable through extensive infill development in the play. Geologically targeted drilling significantly improves project economics and dramatically lowers the threshold oil price required to support project implementation. The results indicate that cost-effective infill development of existing oil and gas fields will increasingly rely on interdisciplinary solutions requiring the expertise of both petroleum geologists and engineers to maximize petroleum geologists and engineers to maximize recovery and economic viability.

Introduction

Reserve growth from the extensive infill development of discovered fields represents a major source of domestic crude oil reserves. Reservoirs in these fields have been often described as relatively homogeneous sandstone or carbonate bodies effectively in contact with wellbores at large (80- to 160-acre) well spacings. In fact, most reservoirs are highly heterogeneous, and at large well spacings, a significant portion of the mobile oil (the oil left in reservoirs as a result of poor drainage by primary production and inadequate sweep by waterflooding) is not effectively contacted.

The degree of reservoir heterogeneity, and therefore the amount of unrecovered oil, is influenced by reservoir genesis. Given adequate understanding of the depositional environment and subsequent diagenesis, reservoir heterogeneity can be related to potential oil recovery. Thus, in order to potential oil recovery. Thus, in order to estimate potential future reserve growth from the infill development of discovered fields, it is necessary to define the depositional settings, to understand how reservoir origin and facies distribution are related to reservoir continuity, and to use this geologic/engineering understanding to evaluate reservoir potential.

This paper examines the economic viability of two approaches for the extensive infill development of fields in the South Central Basin Platform Play; the blanket approach and the strategic approach. The blanket approach to infill drilling assumes that each infill well intersects, on average, a similar volume of previously uncontacted mobile oil.

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