Abstract

Reinecke Field is one of a series of fields in the Horseshoe Atoll (Midland Basin, west Texas) that produce from Pennsylvanian phylloid algal buildups. Examination of cores from the Reinecke Field indicates that porosity in the field is controlled largely by two factors:

1. Leaching of biotic constituents and matrix

2. Dolomitization

These two factors have led to development of a complex reservoir.

Six major rock types have been identified from the field. These are in order of abundance, 1) medium-crystalline, ferroan dolomite, 2) echinoderm-foram wackestone, 3) echinoderm-fusulinid packstone-grainstone, 4) phylloid algal-bryozoan-foram packstone, 5) coarsely crystalline, high-porosity, ferroan dolomite, and 6) shale.

Reservoir porosity and permeability are controlled by the distribution of rock types. In the southern end of the field two areas of differing character occur: one in which the rocks are over 80% dolomite and a second in which the rocks consist of interbedded dolomite and fossiliferous lime wackestone to grainstone. Most of the oil from the field is produced from these two areas. A third reservoir type, which rims the northern half of the field, consists largely of echinoderm-fusulinid packstone and grainstone interbedded with phylloid algal packstone. The remainder of the field has very little data available. Production from the northern half of the field is generally low.

Laterally continuous, high-porosity dolomites appear to be present throughout the field. These dolomites can transmit large volumes of fluid and are responsible for a water breakthrough problem in the field.

As a result of complex variations in depositional and diagenetic facies the reservoir is a laterally and vertically heterogeneous rock body with complex production problems.