Characterization of Lower Eocene Reservoirs in the LL-652 Area, Lagunillas Field - Draft Report

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Date

1994

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Lower Eocene reservoirs (C Members) in the LL-652 area will contain substantial volumes of remaining mobile oil (923 million barrels [MMbbl]) after primary development. This resource exists in poorly drained or undrained reservoir compartments defined by a combination of complex structure and the heterogeneous tide-dominated deltaic facies geometry. The product of this combined structural and depositional complexity are reservoirs that have a high degree of geologic heterogeneity, considerable variation in reservoir quality, and therefore a low recovery efficiency.

The tide-dominated deltaic depositional model of the C Members in the LL-652 area captures a system of dip-elongate distributary-channel sandstones that merge northeastward with extensive, dip-parallel delta-front sandstones. These two facies compose most of the reservoir sandstones and therefore contain most of the remaining oil. Permeability range and average are similar for the major facies. However, there are significant permeability contrasts (up to three orders of magnitude) locally between distributary-channel and tidal-flat, fluvial-estuarine channel and distal delta-front, and distributary-channel and delta-front facies where the base of the distributary-channel facies contains clay clasts that may retard vertical fluid flow.

Diagenesis, not depositional environment, is the main control on porosity and permeability distribution in the C Members. Porosity and permeability in the C Members decrease with increasing depth. In particular, the volume of quartz cement is the main influence on reservoir quality, and because the volume of quartz cement increases significantly with depth, reservoir quality decreases with depth.

The original-oil-in-place (OOIP) resource base of the C Members in the LL-652 area has been increased by 867 MMbbl (60 percent) to 2,318.2 MMbbl. This increase is mainly in the C-3-X and C-4-X Members through documenting additional reservoir area and through improved quantification of petrophysical parameters such as porosity. Extended development through continued pattern infill with 97 new wells will increase reserves from 127 MMbbl to 302 MMbbl. However, an additional 116 MMbbl can be produced from 102 geologically based infill wells strategically targeted to tap areas of high remaining oil saturation by contacting narrow sandbodies that pinch out over distances less than the current 80-acre (1,968 ft [600 m]) well spacing.

A pilot waterflood in the Upper C-4-X Submember in the eastern part of the LL-652 area can recover an additional 70 MMbbl of oil. Expansion of waterflood operations to the entire field could increase recovery by as much as 20 percent of the OOIP, representing a secondary recovery resource of approximately 460 MMbbl.

The LL-652 area is divided into five main and two minor structural compartments. The central structural compartment is the largest production area in the field and includes 76 wells with a cumulative production of 85.8 MMbbl. Seventy-seven percent (66.1 MMbbl) of this production comes from the C-4-X.01 reservoir.

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