A Novel Approach to Compare Pressure Regimes for Compartment Identification in Low Mobility Environment

Abstract

Abstract Formation pressures recorded by Wireline Formation Testers are widely used for identification of compartments based on the pressure regimes. If two virgin zones are at the same pressure regime, it is not a sufficient condition to conclude that they will be in communication during the production life of the field. This is because pressure equilibrium has been attained over geological timescale and the zones may or may not be in communication in the production timespan. But on the other hand, if two virgin zones are found to be at different pressure regime, it can be safely concluded that the zones will not be in communication and thus, belong to separate compartments. While such analysis can be easily carried out for high mobility/ permeability zones, interpretation in case of low mobility zones is often challenging. In low mobility environment the pressures are not very reliable due to incomplete stabilization of buildup and supercharging effects. It is a big challenge to find whether 2 zones have same pressure regimes or not in low mobility scenario. This limitation hinders effective usage of pressure data when formation mobility is low. In the current study, a novel approach has been adopted to analyse the pressures measured by formation testers across multiple zones. For diagnosis of the pressure regimes, a cross plot of excess pressure (Alton Brown et al. AAPG, 2003) versus mobility has been used. This cross plot resembles an exponential decline trend for all the points lying in the same pressure regime. The empirical relationship is supported by analytical models available in the prior literature. Under virgin conditions, the zone whose excess pressure points do not lie on the postulated curve is in all likelihood at a different pressure regime. The workflow has been tested on multiple data sets from various exploratory wells in India. Using this technique, it became possible to identify separate compartments in low mobility environment. For validation, this technique was applied on the data sets where one or two high mobility points were also available. The compartment identification from excess pressure mobility cross plot corroborated with the interpretation based on the high mobility pressure points.