Resistivity-Inversion-Derived Workflow from the Subsurface Uncertainty Management to the Quantitative Reservoir-Scale Profile Update and Well Placement in Reservoirs with Diverse Complexities
Authors: Wan Jun , Wu Xiangjie , Chang Botao , Wang Chao , Li Gong , Wang Fei , Shim Yen Han 
Published: March 2022

At the in-depth development phase, the current horizontal infill campaign in H oil field targets reservoirs with high remaining oil potential and the diverse complexities subject to both structural and lithological controls. These structural and lithological reservoirs are characterized by the uncertainties of formation dip and oil/water contact (OWC), severe stratigraphic heterogeneity, lateral properties change, poor sandstone connectivity, and thickness variation (less than 5 m) of the oil column and interbeds. To effectively squeeze the potential remaining reserves, the scope of the current infill campaign mainly encompasses: (1) the limited crests of the anticlinal traps with uncertain oil column and lateral changed reservoir, and (2) the unexploited marginal areas close to the reservoir pinchout line. Accordingly, it is necessary to quantitatively update the reservoir-scale subsurface profile and execute well placement operations by addressing the above uncertainties with individualized services and workflow.

In these diverse reservoirs, interwell structural and stratigraphic uncertainties are high because resolution of large-scale seismic data and depth-of-investigation (DOI) of small-scale conventional logging data are limited. On these grounds, a high-definition boundary detection service (HDBDS) was employed, which can provide a stochastic resistivity inversion to remotely identify quantitative subsurface features with DOI up to 6 m and resolution of approximately 1 m. Its advantage of balancing resolution and DOI can induce the accurate description of high-definition interwell details, including formation superposition configuration, reservoir pinchout points, and dynamic OWC. Furthermore, HDBDS inversion can combine 3D seismic data and conventional logging data to effectively induce the workflow from subsurface uncertainty management to the quantitative reservoir-scale profile update and well placement.

HDBDS inversion-derived workflow effectively contributed to us achieving our objectives of this infill campaign by generally revealing the high-definition reservoir profiles along the horizontal sections. Up to four boundaries and five layers were mapped simultaneously with a maximum of 3 m distance from the borehole. High coverage and probability of the updated quantitative features induced the higher reservoir profile update rate in these specific environments than that based on the conventional services. In the complex developed areas mainly subject to both structural and lithological controls, the reservoir top, lateral changed properties, and dynamic tilted OWC were quantitatively inverted to identify the effective 1.5- to 3-m oil column, lower than prognosed 5-m column. In the lithological-control reservoirs at block margins, formation superposition configuration, pinchout points, and lateral properties changing features were clearly delineated. Accordingly, the quantitative well placement operations were efficiently executed to distribute the actual smooth trajectory connecting multiple sandstone bodies with the less risk, as well as with maximum standoff to the tilted OWC.

The quantitative results from the inversion-derived workflow could further optimize the completion configuration, waterflooding stimulation efficiency, and well pattern to push development limits as much as possible by efficiently squeezing the remaining oil in these complex structural and lithological reservoirs.