Wolfcamp Formation Reservoir Characterization From Full Diameter Core

Abstract

The Wolfcamp Formation has emerged as a major unconventional resource play in Texas. There is a wide range of oil vs. water production observed in the hundreds of horizontal wells that have targeted this formation. This variability has become a serious challenge for many operators and there is a strong need to understand how to select lateral landing zones to increase oil production and minimize water production. Using slabbed core from the Texas Bureau of Economic Geology (BEG) in Austin, TX, we have used a combination of X-ray CT imaging and 3D FIB-SEM analysis to look for some clues. The well will be referred to as Wolfcamp-1 and is located in the southern Midland Basin. The 168 foot cored interval from Wolfcamp-1 was X-ray CT imaged using a dual-energy method. Dual energy CT imaging allows for the computation of both bulk density and PEF (photoelectric factor) and this information was used to determine rock facies and reservoir quality at high resolution. In combination with spectral gamma scanning, the dual-energy CT data allows for application of petrophysical principles to compute lithology, brittleness, and TOC over the entire cored depth interval. This data was also used to select the exact locations where plug samples were needed to begin to understand the rock characteristics. Additional detailed analysis was conducted on plug samples to define and quantify the key shale reservoir properties including total porosity, connected porosity, organic porosity, pore size distribution, permeability, and the apparent transformation ratio, which is controlled by thermal maturity and kerogen type. The collection and integration of the data from this Digital Rock Physics (DRP) study of samples from the Wolfcamp formation shows that rock types, porosity, and permeability are highly variable and that data from the Wolfcamp-1 well are typical of other Wolfcamp wells we have tested. The DRP analysis further shows that some samples have mostly intergranular pores and while other samples have mostly porosity inside the organic material. Both types of samples may have relatively high porosity and permeability. If we assume that water resides mostly in the intergranular pores and that hydrocarbons are more common in the organic pores, then it suggests that oil production may be increased by targeting the lateral landing zone in the intervals with greatest organic porosity, not just the greatest total porosity.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015