Characterization of Deep Tight Carbonate Gas Plays With an Integrated Interpretation — Case Study From North Kuwait

Abstract

In North Kuwait, the classical deep tight gas play has been tested successfully in two wells with matrix porosity of 5 pu and permeability of 0.01mD but still continues to remain a conundrum in terms of commercial productivity. Though these tight dolomites have proven commercial production from two other wells, where these are naturally fractured. However, natural fractures are limited in extent and observed in few wells only. Hence matrix driven production is of prime importance to develop these tight reservoirs, as these dolomites are extensive in space and time in the entire North Kuwait area. The dolomites are of Mid-Mesozoic Era and are associated with anhydrite and tight limestone in a cyclic deposition of sub tidal to tidal environment. The first drilled horizontal well (1000′) targeted to delineate the matrix driven tight gas play, could not be tested in the targeted dolomite. However, the twin dolomite bodies above it within the argillaceous section were found to be promising as per the SCAL data in the equivalent zone in the nearby well. On testing it produced oil and gas confirming the sustenance of tight gas play. The significance of recent SCAL (XRD, MICP, SEM and Thin sections) and petrophysical SCAL (formation resistivity factor and resistivity index) data from the equivalent cored interval of two adjacent wells enabled to carry out petrophysical re-evaluation of the target zone and argillaceous section. Recomputed fluid saturations showed presence of hydrocarbon based on petrophysical SCAL. MICP data indicated three possible contributing zones within the argillaceous section. These intervals are predominantly dolomites as per XRD analysis. On comparison with global tight gas reservoirs, the closest analogue to North Kuwait tight dolomites appears to be the Atoka Dolomite of Berlin Field of Western Oklahoma, where the average porosity and permeability are in the comparable values of 8% and 0.1 mD at the same depth range with high clay content. In the analogue, acid stimulation in the early stages of testing resulted in formation damage because of the released clays in dolomites. The successful completion adopted in this commercially producing field is hydro-fracturing instead of acid stimulation. The current study has facilitated in understanding the complex lithological assemblages and petrophysical re-evaluation for a possible reserve accretion and need to adopt successful completion mechanism in line with the analogue discussed.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016