Characteristics of Lower Wilcox Reservoirs, Valentine Field, Lavaca County, Texas: ABSTRACT

Abstract

In the Valentine field, Lavaca County, Texas, sandstones of the lowermost Wilcox Group produce oil at depths of about 9,100 ft (2,776 m) in a stratigraphic trap from two sandstones locally called the and zones. Full-diameter cores from the Technik zone show that it consists of thin-bedded turbidites. The Technik reservoir is 25 ft (8 m) thick in a core from the Harkins 1 Mikulenka well. The upper part is composed of thicker beds on the order of 2 to 4 ft (0.6 to 1.2 m), and each displays sequences of massive or massive-to-laminated bedding. These sandstones represent turbidite sequences of the AE and ABE types and were probably End_Page 1595------------------------------ channel deposits. The lower part is composed of thinner beds about 1 ft (0.3 m) thick of more complete sequences which include ripple laminae. These sandstones represent turbidites of the ABCE type and were probably overbank deposits. Some adjacent sandy shales are moderately bioturbated, generally on a fine scale. The Technik nonreservoir facies is 31 ft (9.5 m) thick in a core from the Harkin-Five Resources 1 Cyrus Paul well. The section consists of thinly interbedded shales and turbidite sandstones which are typically incomplete sequences of the AE, BE, and CE types. The shales are not bioturbated. The nonreservoir facies may be characterized as distal overbank deposits. The nonreservoir facies of the overlying Kubena zone is similar. The reservoir sandstones are fine grained (0.17 mm) and contain 59% quartz, 12% other mineral grains, 14% matrix, and 15% kerogenlike organic material. Silica overgrowths and calcite cements comprise an average 13% of bulk volume. Composition results in a relatively low average permeability of 4 md and porosity of 18%. The Technik reservoir sandstone appears to represent the fill of outer-shelf channels along which sands were transported to the shelf margin and into the deeper basin beyond. The nonreservoir facies represents overbank deposits adjacent to channels, but the relation between channel and overbank deposits is not clear. The overbank deposits could have been either contemporaneous, levee sediments adjacent to channel-fill sandstones, or they may represent deposits into which later channels were eroded and then filled. End_of_Article - Last_Page 1596------------