The determination of variogram in the presence of horizontal wells - An application to a conglomerate reservoir modeling, East China

Abstract Building a reliable numerical geological model is critical in reservoir development and management. Inferring a stable 3D variogram is one of the most important processes in the building of numerical geological model. We usually can obtain a well-defined vertical variogram from wells in most cases due to the regular sampling in the vertical direction. The quality of horizontal variogram highly depends on the number of wells, geometric of the well locations, and the trajectory of wells. Horizontal wells usually have preferred trajectory directions due to the geological and geomechanical consideration. As a result, it is very difficult to obtain a reliable horizontal variogram by using the data of horizontal wells. We proposed a three-step procedure to infer the horizontal variogram by integrating geological, seismic, and horizontal well data. We first use the geological information and P-impedance to infer the approximate major azimuth of horizontal variogram. We then obtain the range of the variogram for each horizontal well using the data of horizontal section. We finally determine the major, minor direction and corresponding ranges by least-square fitting the ranges computed using each horizontal well. We illustrate our workflow by applying it to a conglomeratic reservoir modeling, East China. The modeled reservoir properties have a very good correlation with the production data.