Evaluation of regional trends in production for Olmos and Lower Wilcox Lobo trends, onshore south Texas, USA
Creators: name: Waltrip, Nelson William
name: 0000-0003-3897-2801
Publisher: name: The University of Texas at Austin
Year: 2020
Subjects: Olmos
Lobo
South Texas
Tight sandstone
Production analysis
AWP Field
Lower Wilcox

description: South Texas is home to many oil and gas producing geologic formations, including sandstones within the Upper Cretaceous Olmos Formation and Late Paleocene Lower Wilcox Lobo Formation. In the easternmost portion of the Rio Grande Embayment, Olmos Formation deposition occurred in shelf, shoreface, and deltaic paleoenvironments. Similarly, the Lobo formation was deposited in wave-dominated deltaic and shoreface environments in a shallow marine setting. Both plays are tight (low permeability) sandstone reservoirs that have produced significant amounts of hydrocarbons. Production analyses provide valuable insights into how different geologic factors effect production rates. Olmos Sandstone production areas can be differentiated by regional depositional environments. In Webb and Dimmit counties, updip trend reservoirs are characterized by thick, lobate deltaic sandstones while downdip trend reservoirs are thin, sheet-like marine shelf deposits. The AWP Field, located to the northeast, has three distinct depositional environments – delta front, slope, and basin plain environments. By contrast, the Lobo play can be subdivided by gross reservoir thickness across the whole play. Fault blocks related to regional uplift and gravity sliding in the Lobo formation provide a geologic basis to differentiate wells and production. Olmos downdip trend reservoirs, despite having apparently worse reservoir characteristics than those of the updip trend, yield better production results. Delta front reservoirs in the AWP Field have more favorable production trends than slope and basin plain reservoirs due to the superior reservoir qualities. It is hypothesized that the distribution of oil and gas in the AWP Field is a result of the timing of oil and gas generation and migration. Lobo production analyses reveal that thicker Lobo sandstone units result in better production rates. In addition, gas production does not seem to correlate to fault block reservoir volume in the Lobo formation. Base decline rates indicate how well a play or basin is able to maintain current levels of production as hydrocarbons are extracted. Conventional reservoir plays tend to have lower decline rates than unconventional or hybrid plays, where production declines rapidly. Base decline rates for Olmos and Lobo plays show meaningful similarities to and differences with base decline rates documented for the Permian Basin, which has seen an exponential increase in unconventional drilling. While production differences from region to region can be related to geologic factors and controls, production differences also contribute to differing levels of economic viability and exploitation. Since the Olmos and Lobo plays have been developed for decades and are nearing the end of their optimal development life, historical production data is used to build financial models as if each region has not been developed previously. This provides an economic perspective of which regions are better suited for investment and development based on their net present value (NPV) from a discounted cash flow analysis (DCA).