Modeling the Geological Controls on Steam Flood Performance; An Example from a Field in South Oman

Abstract

Abstract A field, located in south Oman, has a compact dome shaped structure with an oil column in excess of 200m. It produces highly viscous hydrocarbon from the fluvial Cambrian Haradh reservoir and represents an opportunity for Thermal EOR development. After an initial phase of steam injection, field data have shown that the response in the trial pattern is not homogeneous. In order to explain these observations a multidisciplinary effort has been undertaken to improve our understanding of the subsurface. The information acquired in and around the injection area (an inverted 7-spot pattern), include connectivity trends from pressure data, temperature surveys, time lapse seismic, cores and well logs. After 20 months of steam injection a thermal response within the pattern is limited to only one producer well and two observation wells. The time-lapse seismic data is consistent with the field data observed from wells in the northern part of the pattern. The pressure data also indicate a predominant North-South connectivity trend within the pattern. Four geological scenario models were built to test factors that may impact the understood distribution of temperature resulting from injection. The modelling workflow intends to assess the impact of 1) the internal structural dip and baffling lithologies within the Haradh Reservoir, 2) faulting within the Reservoir interval, 3) the Carboniferous Al Khlata immediately above the Haradh Reservoir and 4) the variation of Haradh Sandstone Facies and how these may impact fluid flow. The models have been calibrated against historical data so as to ascertain if a given geological realization is a reasonable subsurface representation to reproduce the actual field production and pressure data. The results indicate that an individual scenario does not provide by itself an absolute explanation to the field observations to date. Instead, a combination of scenarios (fluvial facies and faulting) is considered to be a more feasible option to understand the field observations.