Method Integration Improves Reservoir-Property Prediction in East Siberia

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 191673-18RPTC, “Seismic- and Electromagnetic-Methods Integration To Increase Quality of Reservoir-Property and -Saturation Prediction in East Sibera Region,” by Pavel Mostovoy, Roman Oshmarin, and Andrey Ostankov, GazpromNeft, and Olga Tokareva and Daria Orlova, IERP, prepared for the 2018 SPE Russian Petroleum Technology Conference, Moscow, 15–17 October. The paper has not been peer reviewed. This paper describes a case study of the Chonskaya group of fields to demonstrate an approach to the integration of time-domain-electromagnetic (TDEM) electrical and seismic data when building a geological model for improving reservoir-property and -saturation prediction. Introduction The terrigenous sediments of the subsalt complex within the Nepa-Botuoba anteclise are characterized by complex geology: nonanticlinal traps, complex tectonics, lateral reservoir heterogeneity, and digenesis that controls reservoir distribution. The block structure of the Chonskaya group of fields and their poor coverage with exploration wells (Fig. 1) leave a number of uncertainties with regard to water/oil and gas/water contacts in blocks with proved oil content, as well as the main fluid types in exploration blocks. The success of predicting prospective sites for exploration drilling is influenced by minimal risks and reduced uncertainty during field development. An important task at the stage of exploration drilling is to increase the reliability of fluid contacts and reservoir properties. To improve the quality of geophysical predictions during exploration of the Chonskaya group of fields, geological exploration operations were conducted, including 3D seismic surveys and high-density electrical studies [time-domain electromagnetic and magnetic (TDEM)] on a single observation network. The area studied by TDEM and seismic surveys on the observation network in the Chonskaya group covers 3500 km2, more than 50% of the total territory of the license areas. In this regard, the methods to honor the TDEM data when building and updating complex geological models of reservoirs are being actively developed, because the TDEM signal can provide information about fluids saturating terrigenous reservoirs. To understand the capabilities of the technology for integrating seismic and electrical data and making a decision on the basis of the TDEM survey, forward modeling is necessary. On the basis of the modeling results and experience in building complex geological models, the combined use of electrical and seismic data has the potential to be used to separate pure-oil, water/oil, and pure-water zones; to predict probable fluid types in the exploration targets; and to outline zones with poor reservoir properties in terrigenous rocks of the subsalt complex within the Nepa-Botuoba anteclise. A geological model honors the TDEM data through building a geoelectrical reservoir model using a priori geological and geophysical information about target reservoirs—the kinematic and dynamic interpretation of seismic data, well-log-interpretation data, a petrophysical model, and a geological model of the reservoir (2D or 3D). Next, a comparative analysis of the synthetic geoelectrical model with the TDEM inversion data is conducted. The geological model assumptions are revised on the basis of qualitative and quantitative comparison. The revised assumptions allow reduction of the range of geological uncertainties and adjustment of the geological exploration program.