Gas While Drilling-Fluid Reservoir Characterization – a New Geochemical Approach to Characterize Radhuma’s Heavy Oils

Mubarak Al-Hajeri*, Menahi Al-Anzi, B.M. Abbott, Badria Abdul-Rahim, Salah Abdul-Malek, and Mariam Al-Saeed
KOC
*[email protected]

In Kuwait Oil Company (KOC), a geochemical mud log (GML) was developed to help analyze the quality of hydrocarbons associated with the different formations in real time utilizing Haworth’s Ratios as recorded by the gas chromatograph. By using this cost-effective GML tool it is now possible to reliably identify promising hydrocarbon zones. It is also possible to predict the composition and the nature of the subsurface fluids. A relationship has been identified that links total gas counts to the commerciality of accumulations, while GML ratio parameters predict the nature of fluids present. Therefore, integration of the GML ratio parameters with total gas counts can quickly identify potential hydrocarbon zones. When used in combination with drilling rate, lithology and other e-log parameters, the method appears to be a useful method to help select intervals for perforation. Recently, KOC has produced the GML in real-time thereby, helping us prepare and or modify the forward programme. However, with further evaluation we have found that there are some limitations to GML interpretations. During drilling, KOC often uses two types of drilling fluids: water-based mud to drill the section down to the upper Barremian - lower Hauterivian Zubair Formation, whereas, the deeper section is often drilled with oil-based mud. Here we have chosen four exploratory wells A, B, C and D with GMLs distributed across the Greater Burgan field to illustrate the lateral differences in hydrocarbon quality. They are also important in our evaluation of heavy-oil accumulations in secondary reservoirs in the same area such as the Radhuma Formation (Paleocene). Therefore, GML analysis of the gas and or fluid system seen while drilling may indicate higher potential than currently believed. GML evaluation can also provide evidence of: (1) biodegradation and its extent; (2) possible mixing of microbial and thermogenic gases; and (3) the vertical distribution of hydrocarbon quality.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain