Digital Rock Application to refine geological & reservoir models
Enrique Estrada, Barbara Quediman, Rafael March, Santiago Drexler, Milena Siqueira and Jonas Toelke
Pre-salt reservoirs are composed of four main proportion components: calcite spherulites, calcite shrubs, breccia calcite and calcimudstone. These are challenging geological facies to be identified using current borehole Image logs (BHI) available in the industry.
This work presents a methodology to integrate BHI, whole core and plug high resolution medical tomography to overcome this technology limitation. The integration of both techniques allowed using Nurmi classification as a link of the, porosity heterogeneities from images facies (BHI logs) to connectivity and spatial distribution of porous from CT textures (CT Images). As a result, eight (8) CT textures were identified: A) The Mega Shrub represent high-permeability and high porosity with more variated distribution of micro, meso and vuggy porosity. B) Macroporosity represented by reworked grainstone good porosity and permeability. C) Mesoporosity represented by reworked packstone to grainstone intermediate porosity and permeability. D) The Laminated porous represent intermediate conditions of reservoir, with medium to fine porosity and medium permeability. All of these textures represent high-quality reservoir tomofacies that typically develop on a millimeter to 1-centimeter scale and therefore well below the resolution of conventional open hole log data and below the resolutions of the BHI tools. The poor reservoirs rocks are represented by (E) fine laminated, (F) very fine laminated, (G) tight and (H) breccia textures, that occasionally can change to reservoir in the presence of fractures and micro fractures.
This integration supports identification of high-quality plugs for additional petrophysical measurements (RCAL & SCAL). Minimizing the impact of limitations of vertical resolution in image & wireline logs and enhancing the geological model linking Image Log, core CT and Plug microCT to describe facies and texture at different scales provides better understanding of reservoir texture distribution and net to gross.
