The impact of direct measurements of water saturation and water resistivity from core on the hydrocarbon in place calculations of the Azeri-Chirag-Guneshli (ACG) oil field and the Shah-Deniz gas field offshore Azerbaijan

摘要

Uncertainties in water saturations (Sw) calculated from logs have a substantial impact on the hydrocarbons in place calculations for both the Azeri-Chirag-Guneshli (ACG) oil field and the Shah-Deniz gas field in the Azeri South Caspian Sea. For the Shah-Deniz field this is because of the lack of formation water resistivity (Rw) information and the limited textural parameter (SCAL) data during early appraisal. In the ACG field this is because the classical resistivity based water saturation methods significantly underestimate hydrocarbons-in-place. The uncertainties can be reduced by reconciliation of Sw measured directly on core plugs with: 1. High pressure mercury injection; 2. Porous plate capillary pressure measurements; 3. Log analysis based on electrical parameters SCAL and Rw measured on core plug extracts. The process for cutting a low invasion core in synthetic oil based mud is described, as well as the plugging and preservation of core plugs at the wellsite. The derivation of Rw and Sw by direct extraction techniques is also described. Some uncertainties still exist in the direct Sw and Rw measurements on core. Osmotic effects created by the interaction of the mud and the core may impact the accuracy of the direct measured Sw and Rw from core taken in clean sand intervals. Synthetic oil based muds are designed to prevent the borehole from washing out in intervals with a high clay content. This is achieved through dehydration of clays. An experiment to quantify the osmotic effect of synthetic mud on clean sand intervals will be discussed.