Improving Oil Recovery of the Heterogeneous Low Permeability Reservoirs by Combination of Polymer Hydrolysis Polyacrylamide and Two Highly Biosurfactant-Producing Bacteria

Polymer hydrolysis polyacrylamide and microbes have been used to enhance oil recovery in many oil reservoirs. However, the application of this two-method combination was less investigated, especially in low permeability reservoirs. In this work, two bacteria, a rhamnolipid-producing Pseudomonas aeruginosa 8D and a lipopeptide-producing Bacillus subtilis S4, were used together with hydrolysis poly-acrylamide in a low permeability heterogeneous core physical model. The results showed that when the two bacterial fermentation liquids were used at a ratio by volumeof 1:3 (v:v), the mixture showed the optimal physicochemical properties for oil-displacement. In addition, the mixture was stable under the conditions of various temperature (20–70 °C) and salinity (0–22%). When the polymer and bacteria were mixed together, it had no significant effects in the viscosity of polymer hydrolysis polyacrylamide and the viability of bacteria. The core oil-displacement test displayed that polymer hydrolysis polyacrylamide addition followed by the bacterial mixture injection could significantly enhance oil recovery. The recovery rate was increased by 15.01% and 10.03%, respectively, compared with the sole polymer hydrolysis polyacrylamide flooding and microbial flooding. Taken together, these results suggest that the strategy of polymer hydrolysis poly-acrylamide addition followed by microbial flooding is beneficial for improving oil recovery in heterogeneous low permeability reservoirs.

Insights on Water Sources for Injection Development of Large Oilfields in Southeast Iraq and Appraisal of Paleogene Shallow Water Source Formation

As many large oilfields in southeast Iraq entered the final stage of depletion development, water injection appears to be the most economical and technically feasible method to enhance oil recovery. Considering the shortage of freshwater and huge investment in seawater supply project, it is very important to appraise and optimize the favorable shallow water source formation to ensure sufficient water injection supply. Based on regional seismic, well data, core analysis and production test data, Paleogene sequence stratigraphy was determined by integrating well and seismic interpretation. Under framework of sequence stratigraphy, the sedimentary evolution of main water source formations was characterized. Subsequently, combined with core analysis and special logging data, the petrophysical characteristics of the formations were evaluated, and the volume of the regional water source was estimated. The research shows that: 1) Dammam limestone and Ghar sandstone are the two main Paleogene shallow water source formations; 2) Dammama developed carbonate shelf, from southwest to northeast, the formation thickness decrease with the sedimentary evolved from inner slope to out slope. Expose and dissolution increased the porosity which is favorable for water storage; 3) Ghar developed alluvial and delta, from southwest to northeast, the formation thickness increase with the sedimentary evolved from alluvial fan, alluvial river to delta. Delta developed abundant and unconsolidated sandstone with high porosity and permeability; 4) The water sample analysis showed the water belong to Cacl2 type with total dissolved solids greater than 250,000 ppm which indicated well sealing condition. Production tests have shown that both Dammam and Ghar have a water supply capacity of 8,000-10,000 barrels per day. The preliminary evaluation of the water volume in the Ghar area can up to 1 trillion barrels. Paleogene shallow water formation is currently the most realistic and economic water source choice for water injection to enhance oil recovery in large oil fields in southeastern Iraq. Dammam formation and Ghar formation of Paleogene had the characteristics of shallow buried, good water quality and sufficient reserves. Thus, they are the preferred target water source formations for injection development of large oilfields in southeastern Iraq.