Formation evaluation of multiple pay zones within an unconventional reservoir (Permian Basin): An integrated interpretation using elemental, mineralogical, programmed pyrolysis, and mud gas data

摘要

A 3,680 foot (1122 m) vertical Permian Basin well was evaluated using an integrated, multi-instrument dataset acquired while drilling to identify zones of interest for lateral targets. A total of 161 cuttings samples were analyzed to determine the mineralogical (X-Ray Diffraction; XRD), organic (programmed pyrolysis via Source Rock Analyzer), and elemental (Energy Dispersive X-Ray Fluorescence spectroscopy; ED-XRF) composition while gas in air and gas in mud samples were analyzed every foot using a quadrapole mass spectrometer and a Thermal Conductivity Detector (TCD; GC-TRACER™) respectively. Each zone identified as a potential reservoir target exhibits TOC values above 2 wt%, Total Gas (THC %) 3 to 5 times greater than the background gas, T_(max) and methane content (C1%) or C1/THC values suggesting that the reservoir has reached thermal maturity for mixed type Ⅱ/Ⅲ kerogen type determined from Hydrogen and Oxygen Index ratios, and S1 values above 1 mg/g considered adequate for unconventional reservoir production. The zones are further evaluated based on their mechanical properties including bulk mineralogy, calculated Brittleness Index, fluid properties, C1/ROP, and Helium concentration then ranked based on the likelihood of brittle behavior and fractures present during reservoir stimulation. Additionally, conditions most favorable for extensive organic matter preservation during the time of deposition were assessed using elemental proxies such as V, Ni, Mo, and U and were evaluated to further rank each zone by statistical correlation to organic and gas values (regression; R~2). Of the three zones of interest identified, Zone C spanning 650 feet of the lower Pippin, lower Wolfcamp, Cisco and Cline and specifically one narrow target Organic Zone 8 within Zone C was determined to exhibit the best mechanical, geochemical, gas saturation , and elemental characteristics among all lateral targets in the wellbore. This technique of combining sophisticated cuttings analysis with advanced gas-in-mud detection systems deployed at wellsite allowed the operator to make more informed drilling decisions by not only identifying zones of interest but also the ability to rank each zone based on the most favorable mineralogy, mechanical properties, hydrocarbon content and quality, fluid type and maturity, relative permeability, relative water saturation, and paleoredox and organic matter proxies most associated with greatest potential. Additionally, these technologies and techniques can also be employed to determine wellbore position during the build and also characterize the reservoir in the horizontal to better inform completions decisions.