Direct Hydrocarbon Saturation So from Core Plug and Well Cuttings Using Geochemistry Based Method of Extraction-A Cost Optimized Alternative Method for Optimal Test Zone Selection and STOIIP Calculation

Abstract

Abstract We can assess reservoir saturation with high confidence and make timely and cost effective decisions about testing and perforation by measuring hydrocarbon directly on core and cuttings extracts and doing SARA (Saturate, Aromatic, Resin and Asphaltene) compositional analysis integrated with mud log and petrophysical data. Conventional reservoirs usually measure hydrocarbon saturation with petrophysical interpretations based on well log data. But petrophysical methods are often based on resistivity, which is indirect, interpretive and can give unreliable water saturation (Sw) in carbonate reservoirs with complex porosity and different fluid distribution. We have seen that, in many cases, Sw is underestimated, and this causes significant variation in the amount of hydrocarbon in place. Also, the Sw is calibrated by lab measurement of water extracted from core plugs with Dean Stark method. But Dean Stark method can also give misleading Sw, especially when water bound water exists. The aim of this study was to measure oil saturation directly by extracting oil from core plugs. This method has been shown to agree very well with the test results and has potential to provide a more reliable STOIIP and choice of best testing intervals. A suite of more than two hundred (200) core plug samples from different wells were analyzed. Total Extract Yield was determined on extracted samples to assess hydrocarbon saturation through the reservoir of interest. Our method is based on extraction of pulverized core plugs and well cuttings samples. The extracted oil is collected in glass vials, measured in milligrams and is reported per gram of the rock weight extracted. The weight of the oil extracted is then converted, using a mathematical expression, into water saturation (Sw). The approach presented here utilizing extract yield normalized to rock weight has been adopted to assess hydrocarbon saturation. Furthermore, the use of Sw obtained and calculated from extract yield of cores, coupled with conventional open hole logs and mud log, core samples can assist in making time-sensitive drilling and completion decisions, such as selecting optimal perforation zones and identifying high water saturation zones for plugging. Additionally, it can help in keeping horizontal wells within sweet spots and in estimating in-place hydrocarbon volumes in both conventional and unconventional reservoirs. Perforation interval selection or isolation of high-water zone in a horizontal well scenario is particularly very critical in thin and tight reservoirs where improper well completion may severely impact reservoir performance and project’s economics.