Determining Paleostructure from Estimated Ultimate Recoveries

Peter J. Hutchinson

Maps of estimated ultimate recoveries (EUR) for field wells, a qualitative indicator of reservoir porosity and permeability, can represent paleostructure if hydrocarbon emplacement occurred penecontemporaneously with deposition. This type of qualitative understanding from quantitative data can supplement the geoscientist's knowledge of structurally complex fields. Offshore Gulf of Mexico West Cameron 205 field provides an example.

West Cameron 205 field produces from middle Miocene Cristellaria I and Cibicides opima sandstones deposited in inner and outer neritic environments and is projected to produce 310 bcf of gas. Structure maps indicate that the field is a highly faulted, south-plunging anticline. The trapping mechanism is poorly understood: closure, with 1,500 ft of column, is placed anomalously against minor faults; the gas-water contacts and gas columns vary within reservoirs; the structurally highest well is dry; and most of the flank wells are the best producers.

EUR maps indicate that the field was a four-way closed anticline during fill. EUR values can be calculated easily from readily available production data and are not subject to anthropogenic factors that appear in maps of initial absolute open-flow rate or of yearly production. The geoscientist can exploit EUR maps to understand not only field production, but also paleostructure in structurally complex areas.

AAPG Search and Discovery Article #91029©1989 AAPG GCAGS and GC Section of SEPM Meeting, October 25-27, 1989, Corpus Christi, Texas.