An enhanced method for evaluating the static connectivity of reservoirs using pressure coefficient-depth plots

Pressure-depth profiles have been a cornerstone in investigating static reservoir connectivity and compartmentalization since the advent of repeated formation testing tools in the 1970s. The method operates by comparing fluid densities across reservoirs, as indicated by differences in fluid pressure gradients. Discerning pressure shifts requires that the fluids be in the same phase. However, traditional profiles falter in situations with diverse pore fluids due to unpredictable pressure barriers between intersecting trends. Moreover, in normal hydrostatic settings, pore pressure trends often cluster closely, making it challenging to detect minor pressure differences. These limitations introduce uncertainties, thereby reducing the accuracy of connectivity assessments. This paper presents an enhanced method of plotting pressure coefficients against depth. For a given fluid unit, the pressure coefficients show an inversely proportional relationship with depth. The graph depicts a hyperbolic curve that represents fluid pressure variations as a function of fluid density. Differences between the function curves, described by four geometric properties-coincidence, monotonicity, asymptotics, and symmetry-are closely linked to the variable pressure characteristics of compartments. This study provides a detailed analysis of pore pressure data from the Bohai Bay Basin and introduces several case studies. The results show that comparing the geometric properties of functional relationships in pressure coefficient-depth plots significantly reduces uncertainties when assessing static reservoir connectivity, especially in normal pressure conditions and with diverse fluids.