Abstract

The LauraJean #5 core is located in the central part of Upton County, Texas in the Midland Basin along the eastern margin of the Central Basin Platform (Fig. 1). The well produces from the Wolfberry with multiple perforations in the Spraberry and Wolfcamp Formations. A conventional core, totaling 1625 feet, was taken from this well which completely cored the Wolfcamp and Cisco Formations (Fig. 2). The interval from 9923–10210’ was selected to show for the WTGS2010 Fall Symposium.

The Wolfcamp Formation is about 1430-feet thick in this well and composed of equal amounts of shale and gravity flow limestone. The shale is predominantly black or grayish black and rich in clay that is partially siliceous or limey (calcareous). Spicules and other tiny calcareous fossils are relatively common in the shale, indicating the water depth was above the carbonate compensation depth during deposition. Three types of gravity flow carbonates were recognized from the core: debris-flow, turbidity and grain-flow limestones. The debris-flow limestones, making up 90% of the total limestone, are massively bedded floatstone and rudstone. The individual beds range from 0.5-18 feet thick. Three types of debris-flows were identified and subdivided based on the sizes of the particles. The Type I debrisflow is made up of from sand-size to granule-size bioclasts and limestone fragments supported by a siltymuddy matrix. The Type II debris flow is dominated by granules and pebbles. The Type III debris flow is pebble, cobble or greater in particle size. The turbidity limestones are very thin layers of silt-sand grained pack-stones. Fining upward bedding, parallel laminations, and current ripple laminations are common. The grain-flow is a massively or parallel bedded grainstone. It is less common. The grains are bioclasts and rock fragments that range from sand-size to granule-size.

The reservoir rocks in the Spraberry and Wolfcamp Formations are pure limestone with low gamma ray readings. Two potential porosity zones observed in the cores include grain flow limestones (grainstone and rudstone) at 10043’, 10049’, and 10055’-10061’ and reefal bound-stone boulders at 10168-10173’ and 10181-10193’. Interparticle pores and vugs are the main porosity types. The normal debris flow limestones and turbidity limestones are tight and less important for the reservoirs.