Can Diagenesis Restart After Hydrocarbon Emplacement? An Example From the Mauddud Formation, Kuwait

Abstract

The Albian-Cenomanian Mauddud Formation of the Arabian Plate is considered to be one of the most productive oil-bearing reservoirs in the world. The Mauddud Formation in Kuwait is a mixed carbonate-siliciclastic reservoir, capped by an unconformity that is thought to contribute to porosity creation in Sabriyah Field. However porosity in the Bahra Field, which is connected to Sabriyah by a saddle, is pervasively cemented, predominantly by calcite. This study combines seismic, core and wireline petrophysical and diagenetic analysis to determine whether: 1. Cementation by meteoric phreatic cements occluded the porosity in Bahrah before the arrival of oil. 2. Onset and partial growth of the trapping structure in Sabriyah, allowed an earlier oil expulsion to become trapped, retaining secondary porosity, whilst oil bypassed BAMA traps due to later structural growth. 3. E-W fault lineaments in the Bahra Field, which are not present in Sabriyah were responsible for breaching of the seal rock. Leakage may have been followed by an influx burial fluids which re-activated cementation in Bahra The Sabriyah Field exhibits are relatively simple paragenesis, with marine and meteoric calcite cements partially occluding porosity and lined by residual hydrocarbon, suggesting that hydrocarbon emplacement terminated diagenesis. There is some evidence for porosity enhancement after burial calcite cementation the timing of which is uncertain. The presence of a patchy oil stain in Bahrah indicates that it was charged, but residual hydrocarbon is only retained in microporous facies, suggesting trapping by capillary forces. Wide variability in hydrocarbon properties across the field also provide evidence for leakage, particularly around E-W faults. Petrographical evidence of calcite cemented fractures cross-cutting hydrocarbon-stained reservoir rock, and porosity occlusion by burial calcite cements, provides good evidence for ‘restarting’ of diagenesis after hydrocarbon ingress and leakage. These results provide an excellent example of the impact of trap and seal failure on carbonate diagenesis within one of the World's most prolific hydrocarbon provinces.

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