December 6th, 2010

West Qurna, Rumaila & Water Injection (2)

 

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1. The Mishrif reservoirs requires tighter specifications of water quality, our previous laboratory experiments which involved among many tests, flooding full cores at reservoir conditions, led to the conclusion that the size of suspended solids should be less than 5 microns as compared with 10 microns for the Main Pay in south and north Rumaila Fields. The reduction of particle size down to 5 microns could be achieved by using high pressure fields filters at the cluster pump stations, that is when the water is already purified and its particles size reduced to 10 micron at a main water station such as Garmat Ali plant, or reduced in one stage at the main water treatment plant without the need for a high pressure field filters. It’s of course possible to use current injection water that is designed to be injected in the Main Pay. However, Mishrif reservoir rocks are known to be vertically heterogeneous with high variation in porosity and permeability. Using such type of water, i.e with 10 microns, could lead to its injection into high permeability units and thus leaving low permeability layers untapped. Prolonged injectivity tests in selected wells should be carried out as well as observation of the impact of water injection on unit contribution in nearby production wells. The Mishrif reservoirs in Rumaila and West Qurna fields have limited aquifers like most carbonate reservoirs, leading to weaker water drive, hence pressure maintenance is required much earlier than the  sandstone reservoirs like the Upper sandstone member (named Main Pay in Rumaila). This is the reason behind using injection inside oil where the field was subdivided into sectors by water injection wells along lines forming sectors of 5.4 cams width with each sector containing 5 production lines along which production wells are placed. The studies showed that water injection is needed after two years of production. Having said that, production in West Qurna which comes mostly from the Mishrif reservoir can’t be maintained at present time and ramped up in future without water injection.

2. Mr K Al-Mehaidi is totally right regarding the need for good oil field practice. He has mentioned that a similar work in removing restrictions was done in the past in Rumaila and Zubair fields and mentioned reports. Those reports covered laboratory and theoretical works such as differential and flash liberation experiments, flash calculation, well hydraulics, and workover of wells that followed based on those reports. Re-perforation of wells, tubing shortenings, change of christmas trees, replacement of pipelines by larger diameter ones, doubling of flow lines or separating wells from common simple Y piece manifold. Those measures led to larger production rates due either to increase of “KH” contribution in wells in case of perforation or lesser pressure losses in other measures. Reduction in oil quality as a result of changing stage pressure was not acceptable at that time due to its impact on crude oil price at a time of very low oil prices as compared with nowadays, where different crudes with a wide range in API and sulphur content are blended together and sold with compensation for API differential.

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