Integrated Reservoir Modeling on Heterogeneous Ordovician Sandstone of IR-Fields, Murzuq Basin Libya, Helps Optimizing Field Development Plan and Reduce Uncertainty
Authors: Castro Abel , Laksana Sandrya , Abdussalam Gaaim , Allotai Osama , Shaiebi Muhaned , Alkhemri Tarek , Gomez Nacarino Candido , Almhedwi Aljilani , Burghig Faisal , Omar Faiza 
Published: November 2012

The implementation of a methodology to integrate an Asset Team work and generate a field simulation is presented. An approach to a global static and dynamic characterization to carry out a field development plan revision is presented. A general workflow to assess this goal is developed. Structural and stratigraphic model, fine grid construction, facies characterization, properties distribution, geostatistical realizations to manage property uncertainties and building geo-static model are presented together with a complete reservoir simulation.

I&R Fields are located in NC186/NC115 Areas, Murzuq Basin, SW Libya. Two exploratory wells, I-01 and R-01, confirmed oil discovery in Mamuniyat Formation by middle 2005. So far 56 wells have been drilled.

Heterogeneous Ordovician sandstone of Mamuniyat Formation characterizes the I&R-fields where producing oil is a challenge. Generally the formation subdivision consists of Lower (LM), Middle (MM) and Upper Mamuniyat (UM), but the erosion process of MM makes difficult to define their limits. In order to model these reservoirs variability, 11 NMR, 28 imageries, 14 cored wells and 2 SCAL studies were used to response petrophysical properties.

In I&R-Fields, the LM consists of fine to medium grained sands (Phi-avg.: 10.6% & K-avg.: 70mD), deposited SW-NE direction from Fluvial to Offshore environments. UM deposition occurred in a rapid progradation from W-E direction typify the unstable braid-delta front of Fluvial system. The reservoir is typically the best quality facies of coarse-grained to pebbly sands Phi-avg.: 12.5% & K-avg.: 770mD).

3D seismic analysis helps to reduce reservoir uncertainty: (1) generate quantitative and qualitative 2D properties maps to guide the 3D population model, (2) characterize non-reservoir corridors, (3) define the northern stratigraphic limit (4) enhance fault definition. To predict the reservoir thickness and its distribution, hitherto Tanezzuft isochore attribute trend was applied. X-plot of well vs. attributes shows a reasonable result. This technique has been formerly applied to locate producers and injectors wells and lately produced quantitative 2D properties as trend input in 3D model.

Several simulation runs integrating history matching and interactive multidisciplinary work were performed before arriving to the final realization. Predictive runs to develop sensitivity checks on water injection scenarios and additional infill drilling were carried out. A combination of peripheral water-leg, structural-edge oil leg, internal line-drive and infill pattern water injection schemes was envisaged. The proposed revision of the Field Development Plan maximizes the ultimate recovery and requires the drilling of 130 wells (producers, injectors and water source wells) to reach a pick-plateau of 75,000 bopd. Additional wells drilled later on validated the structural and property distribution predicted by the model, as well as the individual productivity indices. Recommendations for additional field data gathering were included in the final report to improve future model updates.