The Wolfcamp shale is a major oil and gas producing formation in Texas. Oil production from the Permian region is now over 2 million BOPD despite large declines in rig count over the last 12 months (EIA, April, 2016). The Delaware Basin is contributing an increasing share of Permian production. The well analyzed for this project was drilled in 2014 and had a full diameter core sample of about 247 feet in length. Dual-energy CT (DE-CT) scanning and spectral gamma logging was used to compute mineralogy and TOC along the core. Over the same vertical interval, drill cuttings were acquired at a sample interval of 5 ft. Drill cuttings were also acquired at 30 foot intervals along the lateral portion of the wellbore. Wireline log data obtained on this well includes quad combo, spectral GR, image log, elemental components log, and a full wave sonic. This data has been used to compute fluid and volumetric properties as well as rock mechanical properties.
A major goal was to quantify total porosity (PhiT), effective porosity (PhiE), porosity associated with organic matter (PAOM) from core samples and use this data to aid in interpretation of the wireline log data. The subject well was drilled in Culberson Co., TX and will be called Wolfcamp 1. This well was chosen to serve as a science well and is one of several wells drilled on behalf of the same lease holder. As such, a comprehensive core and well log analysis program was and executed by Halliburton Inc. of Houston, TX and several core analysis, digital rock, and geochemistry service labs. The zone of interest was in the upper Wolfcamp A.
This project involved the integration of data from about 247 feet of whole core, drill cuttings sampled every 5 feet over the zone of interest, and a comprehensive suite of open-hole well logs. The log display over the cored interval is shown in Figure 1. In the Wolfcamp, PAOM is interbedded with inter-granular porosity and most of the hydrocarbon resource is likely to be stored in the PAOM. Ion-milled SEM data and 3D FIB-SEM data was used to obtain PAOM, pore size, and permeability from about 30 plug samples.
Core and drill cuttings
Full diameter core was shipped in sealed aluminum tubes from the well site to the digital rock lab. The core was imaged with a modern medical X-ray CT scanner in dual-energy (DE) mode. The DE-CT scan data was processed to compute bulk density (RHOB) and photoelectric effect (PEF) using a method described by Vinegar, 1986 and Coenen and Maas, 1994. The core RHOB and PEF curves were calibrated using known material standards and it was observed that the core data were generally consistent with the available open-hole well logs. In parallel, the samples were scanned with a spectral gamma logger to measure the natural gamma emissions from thorium, potassium, and uranium.
