Research On Oil-based Drilling Fluid Protection For Fractured Tight Sandstone Reservoirs

This thesis takes the fractured tight sandstone reservoir in Yingshan block as the research object and analyzes the reservoir characteristics and potential damage mechanism..On this basis,a set of white-oil-based drilling fluid system suitable for the reservoir characteristics of this block was developed in the laboratory,and the damage characteristics of this system to the fractured reservoir in Yingshan block were deeply analyzed.Based on the damage characteristics,corresponding protection measures were proposed,thus forming an oil-based drilling fluid system with good reservoir protection performance.Firstly,the lithology,physical properties,pore throat characteristics and fracture distribution of the Yingshan block are analyzed.The results show that the average porosity of the reservoir is between 3.62%and 4.33%,and the permeability is between 0.0001×10-3 ?m2 and 1.3040.×10-3 ?m2.The pore throat connection is poor,and the clay mineral content is medium.Among them,illite is the main part,and some of it contains iridium/montmorillonite.The crack width of the reservoir is mainly concentrated within 100 ?m.Based on reservoir characteristics analysis,also combined with reservoir sensitivity and water lock experiment,it is concluded that sensitivity damage(water sensitivity damage,salt sensitivity damage,alkali sensitivity,stress sensitivity damage),water lock damage and liquid phase damage are the main causes of reservoir damage.On the basis of clarifying the reservoir characteristics and damage mechanism,the indoor key treatment agent for oil-based drilling fluid was optimized and compounded to form a set of white oil-based drilling fluid with a density of 1.20?2.00 g/cm3.The specific formula is 5#white oil+20%calcium chloride saline+3%-4%composite emulsifier(EMU-3:EMU-4=3:4)+0.5%?1%auxiliary emulsifier FRHJ-3+1%?2%wetting agent WET-3+2%?3%water loss reducer(FL Z-ZR:HY=1:1)+2%-3%organic soil 5+2%calcium oxide+barite.In order to determine the applicability of the system,the basic performance was evaluated.The evaluation results show that the system has a temperature resistance up to 210? and the demulsification voltage is about 1000 V with good emulsion stability.Anti-pollution performance,thermal stability and inhibition.and suspension stability is all good,meeting the needs of drilling and completion work in Yingshan block.The damage characteristics of the white oil based drilling fluid to fractured reservoirs in Yingshan block are studied.The results show that the main damage of the system to fractured reservoirs is the blockage of the oil in water emulsion and the gas-liquid multiphase flow effect of emulsion demulsification,the change of oil lock,the wettability of reservoir,and the blockage of solid particles.Taking the prevention and reduction of oil-based drilling fluid liquid invasion and solid phase invasion as the breakthrough point to protect fractured reservoirs,the laboratory reservoir protection experiments were carried out.The reservoir protection formula is formed as follows:white oil-base drilling fluid+1.5%?3%fiber HLF+4%?5%compounded with different mesh of calcium carbonate+2%?5%micromanganese ore powder+0.5%FEP variable filling particles,which has good reservoir protection effect,permeability recovery rate of about 90%,forming tight sealing zone and bearing capacity of 5?7 MPa.This paper systematically expounds the potential damage mechanism of fractured reservoirs in Yingshan block,analyses the damage characteristics of white oil-based drilling fluid to fractured reservoirs,and forms a well-protected white oil-based drilling fluid system,which provides technical support for the application of oil-based drilling fluid in fractured tight sandstone reservoirs in Yingshan block.