Research On Fractured-cavity Carbonate Reservoir Damage And Completion Fluid In H Oilfield

In the process of drilling and completion,damage to the reservoir is often caused by various reasons,among which drilling and completion fluid damage is one of the most important factors.Halfaya Oilfield has 9 reservoirs with high permeability and low permeability,among which carbonate reservoirs contribute more than 80%of production.On the one hand,for the reservoir damage of fracture-cavity type carbonate rocks,stress damage and water lock damage are mainly studied,and the basic theory mostly comes from the porous sandstone formation.On the other hand,the type of carbonate reservoir in the Halfaya Oilfield is very special.It is different from the conventional porous sandstone and carbonate reservoirs.The main reservoir spaces are intragranular pores,mold pores,and dissolved pores.The main percolation channels are the fractures and micro-fractures that connect the pores.The lithology is mainly composed of the Cretaceous argillaceous limestone carbonate reservoirs.It contains a large amount of calcite and is basically free from dolomite,and the reservoir is highly heterogeneous.The reservoir damage mechanism cannot simply copy the damage mechanism of domestic carbonate reservoirs.Therefore,a targeted study of this block is conducted to study the reservoir damage mechanism,and it is necessary to propose a protective completion fluid system for reservoirs.Through research and analysis,it is found that there are moderately strong acid-sensitive damage and stress-sensitive damage in the reservoir,and there is a moderately weak speed-sensitive damage.The speed-sensitive damage rates were 55.48%and 5.59%,respectively,with an average of 30.54%.The degree of damage was moderate and weak.The reservoir hydrochloric acid and acid-acid sensitivity were 51.40%and 54.05%,respectively,and the degree of damage was moderate and strong.The stress sensitivity of the reservoir matrix core is moderately strong,and the fractured core is highly sensitive to stress and is irreversible damage;there is a strong water lock damage in the reservoir;solid particle clogging damage is a major factor in reservoir damage;during drilling Well leakage also causes damage to the reservoir;inorganic scale is also a major cause of reservoir damage.Based on the reservoir damage mechanism in this block,the formate brine was established as the completion fluid system for the protection of the carbonate reservoir in the Halfaya Oilfield Through a single-agent screening,the well completion fluid formula for the reservoir was determined as:Clearwater + 0.3%Na2CO3+0.5%PAC-HV(tackifier)+ 1.0%XC(tackifier)+ 1%SMP-Ⅲ(fluid loss reducer)+ 3%Redu2(fluid loss reducer)+ 2%CSI(clay stability agent)+ 2%CY-1(film former)+ 0.002%POCA(antiscalant)+ 4%CS(corrosion inhibitor)+0.1%FSSJ(waterproof lock)+ HCOONa.The performance test shows that the system has good performance,strong system stability,density adjustable between 1.00～1.30g/cm3,anti-temperature energy up to 140 ℃,salt,calcium,anti-cutting debris pollution ability,storage The layer protection performance is good,and the reservoir permeability recovery rate can reach more than 85%.It is a high-quality completion fluid system suitable for carbonate reservoirs in the Halfaya Oilfield.