Pinpointing Reservoirs from the SkyThu, 12/14/2017 - 12:40
Q: NXT offers geophysical exploration services in the upstream segment. How does your patented Stress Field Detection (SFD) technology work?
A: SFD uses a reservoir-scale gravitational detection method to rapidly identify and rank prospect-level leads to focus exploration efforts, particularly in frontier and underexplored sedimentary basins. It is an independent reconnaissance tool for analyzing the presence of a valid trapping configuration in a variety of geological settings, such as structural or stratigraphic traps in conventional exploration as well as anomalous fluid trapping conditions in unconventional regimes, such as shale gas and tight oil.
In general, porous rocks and the presence of fluid cause a decrease in bulk density, which will produce a gravitational low. If more fluid is accumulated in a trap with high porosity, then the reservoir system becomes more homogenous provided there is adequate permeability distribution. This results in greater spatial subsurface homogeneity. In addition, the redistribution of principal stresses also plays a significant role in the development of subsurface conditions associated with discontinuities. Investigations of gravity gradients and stress changes have shown that there is a physical relationship between the two at small scales and these changes can be detected using gravity as a proxy.
The subsurface geological condition required for SFD to detect gravity field perturbations due to stress variations in the horizontal direction is the occurrence of a structural and/ or stratigraphic change with sufficient difference in elastic properties. An important source of elastic variations is the presence of trapped fluids. Other sources include faulting or fracturing, over-pressure, major lithological changes and basin boundaries; generally, all major discontinuities will evoke a distinct SFD response.The gravity field includes fine spatial-scale perturbations or distortions that arise from a combination of density and stress effects. Based on extensive observations and investigated correlations with other geological and geophysical data, SFD data has proven highly effective in identifying potential hydrocarbon traps in a wide variety of geological settings, including thrustfold belts, foreland basins, subsalt plays and extensional regimes.
Q: How did your proof of concept with PEMEX in 2012 develop?
A: The initial survey that NXT conducted for PEMEX in fall 2012 focused on two objectives. First, a “blind” test of the SFD system over areas with significant proprietary G&G information, and second, identifying new prospective areas in the region. The survey area is geologically complex and covers the Salina del Istmo, Salina del Istmo Deep Gulf portion, Reforma Akal Pilar, Macuspana basins as well as the Sierra de Chiapas area and the Yucatan Platform. The sediments of these basins are terrigenous, carbonates and in some areas, salt bodies are present. The program was conducted in two stages; the first program of approximately 3,200km was flown and PEMEX compared the initial results with its proprietary data. As a result, an additional 750km of SFD was acquired to increase data coverage within a particular area. The PEMEX-conducted integration results show significant correlation between SFD anomalies and known hydrocarbon accumulations. The designed lines crossed a total of 64 known hydrocarbon accumulations of various sizes. PEMEX determined that SFD successfully identified 47 of these known accumulations. These 47 locations represented over 95 percent of the reserves flown over in the survey region. The remaining unidentified accumulations were largely isolated features with linear extents below 2km.
Q: How does the use of SFD affect the possibility of striking oil?
A: According to various statistical reports, the exploration success rate for wildcat wells varies from 18 percent in onshore exploration to 7 percent in offshore exploration. Wildcat drilling success rates increased to greater than 60 percent in areas where SFD was used in conjunction with seismic programs.