Effects of Geologic Heterogeneity on Waterflood Efficiency at Jordan Field, University Lands, Ector and Crane Counties, Texas

R. P. Major, M. H. Holtz

Jordan field produces oil from the Permian (Guadalupian) San Andres Formation at a depth of approximately 3,500 ft on the east flank of a low, broad anticline located on the eastern side of the Central Basin platform in the Permian basin of west Texas. Since discovery in 1937, the portion of the field on university lands has produced 68 million of the 175 million bbl of original oil in place. An estimated 55 million bbl of mobile oil remain in this reservoir.

The upper San Andres Formation at Jordan field comprises approximately 400 ft of upward-shoaling subtidal to peritidal carbonate strata now thoroughly dolomitized and partially cemented by sulfates. Peritidal facies are nonporous mudstone and generally nonporous pisolitic packstone and grainstone characterized by abundant sulfate cement. Where sulfate cement is either leached or absent from fenestrae, the pisolitic rocks are locally porous and permeable. Subtidal facies are primarily pellet grainstone containing fusulinids and crinoids; local bioherms composed of bryozoans, algae, and corals; and skeletal grainstone composing associated flanking beds. The lower subtidal section is characterized by a stratigraphically distinct zone that has been diagenetically altered by a postburial l aching event. This diagenetic alteration has increased permeability.

The reservoir may be divided into three petrophysical zones: (1) an upper zone of peritidal facies that is locally porous and permeable; (2) a middle zone of pellet grainstone with moderate interparticle porosity and minor moldic porosity; and (3) a lower zone of diagenetically altered (leached) pellet grainstone and skeletal grainstone with interparticle porosity and high permeability. Production history plots reveal that numerous wells have floodwater cycling problems. Injection profile data indicate that although most well bores are open to the entire formation, most floodwater is injected into the lower zone and locally significant amounts are injected into the upper zone. Injection in the middle zone is rare, suggesting that this zone is incompletely swept due to channeling throu h the more permeable upper and lower zones. Selective well-bore plugging and performation squeezing may focus injection water into the middle zone, thus producing by-passed oil that otherwise would be left behind.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.