Sand Bodies Connectivity Analysis Utilizing Measured Pore Pressure in Normal Pressure, Offshore Bohai Bay Basin, China

Abstract

Due to the consistency of pressure system within a uniform reservoir, the pressure-depth plot is currently deemed to be an important criterion to determine the connectivity of sand bodies in normal pressure reservoirs. However, because of the influences of high permeability and fluid heterogeneity in the oil reservoir, the linear rule used to estimate the sand bodies connectivity has its limitations. For instance, there exists relatively lower crude oil density and viscosity as well as higher conversion formation pressure on the top of oil column and that will influence the linear relationship of the pressure-depth plot resulting in erroneous connectivity identification. Applying mathematical induction, an advanced method for sand bodies connectivity analysis is proposed. The specific approach is building the relationship of pressure coefficient versus depth through formula derivation transforming the linear relation between the pressure and depth into the inverse proportional function. The properties of inverse proportional function such as intersection, monotonicity, boundedness and symmetries provide us a new way to explore the relationship between the reservoir depth and pressure system and furthermore determine the connectivity of two or more sand bodies. We have verified the relationships between the sand bodies connectivity and the properties of inverse proportional function of the pressure coefficient versus depth in more than 50 normal pressure reservoirs out of 7 oilfields in offshore Bohai Bay Basin, where the connection of sand bodies has been confirmed by actual development wells. The conclusions are as follows: 1)the function image being continuous and overlapping, monotonicity and asymptote being consistent, and symmetry axis being unique are the critical criteria for determining the connectivity of the consecutive sand bodies; 2)the pressure coefficient is more sensitive and reliable than the linear function; 3)the curvature of the inverse proportional function is affected by the reservoir permeability and fluid properties, thus it overcomes the limitations of linear rule. The prediction accuracy of the sand bodies connectivity has improved significantly utilizing the inverse proportional curve of the pressure coefficients versus depth which also reduces the geological risk and uncertainty, and provides a reasonable support in field development plans design.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017