Productivity Control Mode of Reperforation in Complex Multi-layer Porous Carbonate Reservoir

The Rumaila formation of Ahdeb oilfield in Iraq was a typical complex multi-layer porous carbonate reservoir in the Middle East, which including Ru2a, Ru2b-U, Ru2b-L1, Ru2b-L2 and Ru3, developed from top to bottom. Due to the comprehensive effects of multiple reservoir types, complex oil–water relationships, strong reservoir heterogeneity, multi-layer combined production and casing channeling, a series of problems such as prominent inter-layer contradiction, low recovery rate and high water cut rise rate have been caused. Based on the recognition of geological reservoir, a six criteria method of “combing reservoir, formulating standard, guaranteeing oil bottom, distinguishing casing channeling, making strategy clear and understanding production control mode” had be established to effectively solves the problem of the productivity control mode of realizing medium and high production of replacement. Research shows: ①Ru2b-L2&Ru3 formation should be avoided perforating to evade the high permeability strip at the top of Ru3 formation, asphalt cushion at the middle and upper part of Ru3 formation, strong bottom water coning and casing channeling which had caused the increase of water saturation and low production in the upper reservoir of Ru2b-L2&Ru3 formation; ②Ru2b-U layer could be fixed as the priority perforation layer, Its KH value should be considered to be the main control factor of production capacity, the top of U1 + U2 + U3 was determined as the optimal perforation section on the basis of defining the reservoir overlay mode and safe oil bottom interface; ③The combined perforation model with Ru2b-U formation as the main part and Ru2a-5 and Ru2b-L1 layer as the auxiliary had be established and the dynamic characteristics of production under different modes had be determined. It is concluded that vertical well pattern replacement measures could obtain higher production and lower water cut, and its development experience should be worthy of reference for similar reservoirs.