Lost Circulation Control With Oil Based Drill-in Fluid For Ultra Deep Tight Sandstone Gas Reservoir

Ultra deep tight sandstone gas reservoir with high temperature and high pressure,low porosity and Ultra-low permeability,fracture developed,abnormal formation pressure and high damage potential and so on.In the process of drilling and completion,drill-in fluid leakage is caused by the developed fractures which is one of the most serious potential damage factors.Before drilling the reservoir,prior to adding the solid particles which are matched with the reservoir fractures,The organic combination of lost circulation control and lost circulation prevention when drilling reservoir section,reduce drill-in fluid leakage damage,effectively protect reservoir which has important significance.Taken the J、W area as the research object in the Ultra depth tight sandstone gas reservoir in the Tarim Basin,describes the geological characteristics,confirm the reservoir dynamic fracture width;assessed the oil based drill-in fluid lost circulation control performance,developed the plugging material evaluation experiment for Ultra deep well drilling,optimized plugging material which is suitable for the J、W area engineering geological condition;design and assess the oil based drill-in fluid optimization formula;the optimized formulation was applied to 2 trail wells on J、W area,the effection of lost circulation control is perfectly;Enriched plugging material optimum index of Ultra deep well,improve plugging material of the Ultra deep well drilling optimum strategy.The main performances as follows:Clarified the range of reservoir fractures static and dynamic width.By using the finite element method and the dynamic inversion method,get the static and dynamic fractures width.J area the static fractures width is no more than 500μm,W area the static fracture width is no more than 100μm.Under the influence of the positive pressure difference of the drill-in fluid column,the dynamic width of J area reservoir fractures is 200μm to 2000μm;and the leakage width of the W block is 300μm to 3000μm.Evaluated the reservoir protective performance of original oil based drill-in fluid.Carried out the oil based drill-in fluid static damage evaluation,results show.that oil based drill-in fluid average damage rate is as high as 62.77%on the fracture core.The dynamic damage evaluation experiment shows that the permeability recovery rate of the oil based drill-in fluid is only 37.87%under the condition of the small flowback pressure for the fracture which is less than 50μm.The evaluation of plugged layers pressure-bearing capacity shows that the original oil based drill-in fluid only can effectively seal the 100μm fractures,and almost no plugging ability to the fracture of 150μm and above.Summary,the original oil based drill-in fluid is poor for the lost circulation control and the reservoir performance protection.Improved the optimization method of plugging material for Ultra deep well.After evaluate the particle size distribution and the acid soluble rate,we select KGD-3 and Walnut shell as the representative,to carry out high temperature aging,aging pressure,abrasive and friction experiment.The results showed that the walnut shell have low acid solubility,high carbonization after aging,and the pressure bearing capacity decreased seriously.However,KGD-3 with its high acid solubility,excellently performance of pressure bearing capacity when high temperature aging,which is more suitable for Ultra deep lost circulation control.Formed an oil based drill-in fluid formulation with temporary plugging function.Based on the idea of temporary lost circulation control technology,carried out the formulation of oil based drill-in fluid optimize,and try to combine calcium carbonate particle and KGD series materials which design the formula according to the orthogonal experimental method.The results show that the formula J-7(Oil base drilling fluid +1%CaCO3(2250 mesh)+5%KGD-2+3%KGD-3)can effectively plug 500μm wide fracture width;the formula W-3(Oil base drilling fluid+1%KGD-1+5%KGD-2+3%KGD-3)can effectively plug 1000μm under the pressure difference of 10MPa,which can reached the requirements of the oil field.The basic performance of the optimized formulation is stable,and the recovery rate of permeability is 69.20%.By 2 wells trail in the field,the amount of lost circulation decreased greatly,and the lost circulation control effection is perfectly.Riched plugging material optimization index in the Ultra deep fractured reservoir..For high temperature high pressure and oil based environment in Ultra deep fractured reservoir,plugging material evaluation of the experimental results of high temperature aging,friction and abrasion,rich plugging material optimize index in Ultra deep fractured reservoir,and based on the importance of index,divided into three grades,and draw the Ultra deep fractured reservoir plugging material optimization strategy table.