Perforating Fluid System Development And Evaluation For Low Permeable Formation

Block Xing 8-12 in Daqing oil field is argillaceous siltstone with lowpermeability. The undeveloped formation results in poor water-intakecapacity and thin water-intake thickness,and average content of dirty sand is12.35%, and air permeability is 0.025 um2. According to the standard of fieldappraisal, the target zone belongs to laminated layer. So reservoir protectionis very important during the course of well completion. In this case, researchon perforating fluid for low permeable formation in block Xing 8-12 zone ofDaqing oil field is carried out. This project has been a part of field test aboutreservoir protection in the course of well drilling and completion.The research on novel perforating fluid for low permeable formationfocuses on clay stabilizer based on clay content analysis and reservoirsensitivity. We start with clay swelling principle and water sensitive mineralanalysis to optimize clay stabilizer through fragmentation, compatibitity andswelling experiments, and then screen out weight agent, demulsifier andantiseptic to determine the perforating fluid system. Conventionalperformance evaluation and core damage test have also been finished. Nowgood field application results have been achieved. This technology has greatsignificance for low permeable oil reservoir development.1,Reservoir sensitivity evaluation for Block Xing 8-12 in Daqing oilfield1.1Geologic research for transition zone in block Xing 8-12The target zone of secondary infill wells and additional wells in Xing8-12 transition zone is thin layers of SⅡ, SⅢ,PⅠ. Untabulated reservior hasmore silty sand and dirty sand, which is 72.77% and 12.35% respectively;airpermeability is 0.025 um2, average porosity is 21.35%.1.2 Water sensitive mineral analysis for laminated layers in Xingnan oil fieldThough X-radial diffraction, there are four clay minerals in SⅡpayzone, they are illites, kaolinte, mixing layer of illites and montmorillonite, andmixing layer of chlorite and montmorillonite, and absolute content of claymineral is 14.10%, among which, average relative content of illites is 66%.According to the standard of field appraisal, the target zone of secondaryinfill wells in Xingnan belongs to poor oil layers.1.3 Formation sensitivity evaluationVelocity sensitivity experimental results table1CoreCriticalflowrate(ml/min)permeability10-3μm2VelocitysensitivityindexVelocitysensitivityclassificationXing 8-30-319-1 0.25 0.047 0.18 WeakXing11-2-J375-1 0.50 0.190 0.40 MediumXing11-2-J375-3 1.90 3.35 0.40 MediumXing11-2-j375-5 3.42 8.97 0.08 WeakXing11-2-j375-7 3.57 11.71 0.16 WeakXing11-2-j375-8 1.25 2.91 0.59 MediumWater sensitivity experimental results table2CoreInitialpermeability10-3μm2permeability withdistilled water10-3μm2watersensitivityindex rwatersensitivityclassificationxing11-2-J375-2 1.30 0.415 0.680 Middlingxing11-2-J375-5 6.25 2.49 0.602 Middlingxing 13-J2-P336-5 24.33 14.31 0.412 Middlingxing11-2-J375-9 29.40 19.29 0.344 Middlingxing11-2-J375-4 35.03 23.01 0.343 Middlingxing11-2-J375-1 64.76 45.13 0.303 Middlingxing 13-J2-P336-2 74.78 49.88 0.333 MiddlingVelocity and water sensitivity experimental results for well Xing 8-30-319and Xing11-2-J375 are listed below.2,Study on perforating fluid system for low permeable formationClay stabilizer is essential for water-sensitive formation, so research onclay stabilizer is the key point of this project.2.1 Performance EvaluationWe compared four common perforating fluids (1#,2#,3#,4#) in terms ofaspect, density, pH, mean grainsize, swelling ratio, corrosion rate andsuspending solid content .2.2 Study on perforating fluid system for low permeable formation2.2.1 Clay stabilizer classification2.2.1.1Chemical that can reduce clay surface electronegative2.2.1.2 Chemical that can act with hydroxyl on the surface of clay2.2.1.3 Chemical that can change mineral type2.2.1.4Chemical that works through the properties of clay surface and theformation of chemical bond2.2.2 Clay stabilizer evaluation2.2.2.1Evaluate by the ratio of upper limit to lower limit of interplanar spacingd0 of Ca montmorillonite2.2.2.2 Evaluate by shale dilatometer2.2.2.3Core debris crushing ratio2.2.2.4Core damage rate2.2.3 Clay stabilizer screening experimentsFragmentation, compatibitity and swelling experiments were carried outto optimize clay stabilizer, which is the combination of 2% 4# clay stabilizingagent and 2% NH4Cl,Experiments indicate crushing rate of core debris is1.57%,swelling rate is 14.66%。2.3 Demulsifier screeningTwo ommon demulsifiers, 1#and 2#were evaluated. Demulsifying ratio is100% when concentration of demulsifier was 0.2%2.4 Weight agent screeningBased on well completion design, we confected perforating fluid withdifferent density. We chose NaCl as weight agent, and the density ofperforating fluid was 1.02g/cm3 in experiment.2.5 Antiseptic screening3# antiseptic has obvious corrosion inhibition effect. The corrosion ratewas 0.016 g/m2.h with 0.2% 3# antiseptic, and the blank sample was0.046g/m2.h.2.6 Perforating fluid determinationFormula: 8 % NaCl + 2%4 # clay stabilizer+2% NH4Cl+0.2%1 #demulsifier+0.2%3#antiseptic2.7 Core displacement testAccording to the results, core damage rate was 7.84% by using novelperforating fluid, which is 26.97% lower than fresh water. It shows optimizedperforating fluid can meet the need of laminated reservoir.3.Field applicationThis technology has been applied for 45 wells, in contrast to the blankwells, this protection measure can mitigate the damage during the course ofcompletion.4.Conclusion4.1 The target zone of Xing 8-12 transition zone is untabulated layers andtabulated thin layers of SⅡ, SⅢ,PⅠ. Untabulated reservior has more siltysand and dirty sand. According to the standard of field appraisal, it belongsto laminated layers. Sensitivity evaluation tests indicate, water sensitivityindex increases with the decrease of formation permeability, and oil fielddevelopment is affected more seriously, so reservoir protection is essential.4.2 The research on novel perforating fluid for low permeable formationfocuses on clay stabilizer, and then weight agent, demulsifier and antisepticare chosen to determine the formula of perforating fluid system. Experimentsindicate crushing rate of core debris is 1.57%,swelling rate is14.66%,corrosion rate is 0.016 g/m2.h, and demulsification rate is 100%.4.3 Newly developed perforating fluid system has much lower damage rateof 7.84% compared to four common perforating fluids, so it can protectreservoir and prevent secondary pollution.4.4 This technology has been applied for 45 wells, in contrast to the blankwells, injection pressure is decreased by 0.1MPa, and injection rate isincreased by 10.3m3, injectivity index is increased by 0.05m3/d.m.MPa. Sothis protection measure can mitigate the damage during the course ofcompletion.