Study On Optimization Design Of Perforation Negative Pressure

High transient flow can flush out debris from perforation tunnelimmediately after perforation with proper underbalance pressure which is created by dynamic underbalance pressure tool or static underbalance pressure. As the key point of the underbalanced perforating operation, minimum underbalance pressure is postulate of perforation cleanup and directly affects the quality of perforating operation. Though itcan be obtained by many design methods, these methods are either empirical equations or semi-empirical equations which can’t be used comprehensivelybecause they take few factors into account, results from these equations are totally different and hard to choose.Underbalanced surge flow model was established with permeation fluid mechanics and hydromechanics to study the high transient flowing. To obtain the theoretical minimum underbalance pressure, this paper also studied the flow field and debris moving track in the perforation tunnel during high transient flow with FVM (Finite Volume Method). In addition, how Damage skin, threshold pressure and flow friction in horizontal wellaffected the high transient flow was analyzed, the three factors were considered to optimize minimum underbalance pressure design method. According to the situation of oilfield and Combining maximum underbalance pressure from Colle method and theoretical deducing equation for sand control, a rational underbalance pressure design method was established. At last, the rational underbalance pressure was verified according to compression strength of downhole tube, rock stability and perforation stability.Based on the previous study, factors for minimum underbalance pressure design were analyzed.Being different with traditional conception, study shows that minimum underbalance pressure can be affected by parameters of perforating operation like perforating depth, perforating density, tunnel diameter, etc.Because percolating interference and percolating condition change as these parameters vary.Permeability is the main factor which should be considered during underbalance pressure design, and minimum underbalance pressure will increase as permeability reduce. Meanwhile formation damage caused by well drilling and crush zone badly decrease the permeability of the rocks around the wellbore,minimum underbalance pressure will increase as damage skin increases. Underbalanced perforation in long horizontal section will cause great friction pressure loss, greater underbalance pressure is required for longer horizontal section and perforation section. Relatively speaking, the effect from threshold pressure is extremely small.Experimental application of this new design method was successful. According to the field data, underbalance pressure from this design method can createsufficienttransient flow to flush out debris from perforation tunnel, enhance the oil productivity greatly. It also met the requirements against formation sanding and tube failure. Compared with traditional underbalance pressure design methods, the new design method takes comprehensive factors into account, result from this method is scientificand rational.