High-Density Low-Damage Solid-Free Testing Fluid Research And Development

With the continuous exploitation of oil and gas resources onshore,many oil and gas fields begin to show a trend of declining productivity.It is very urgent and important to explore new fields of oil and gas development.Deep-sea oil and gas came into people's sight.A dense gas reservoir in the east China sea has billion tons substantial production,but its main gas formation has the characteristics of high temperature and high pressure,with pressure coefficient as high as 1.8 and temperature 160?,and predictably,with the deepening of the deep sea oil and gas development,the reservoir temperature and pressure coefficient will rise further.Formation testing is a very important work in the process of oil and gas exploitation.There are few solid free test fluids for HTHP reservoirs at present,focusing on the highly corrosive and highly toxic bromine zinc salt system,or the extremely expensive cesium formate test fluids.These test fluids cannot be used well in the deep sea development process.Therefore,this paper is committed to developing a new high-density solid-free low-damage test fluid,which is different from the above test fluids system,to meet the challenge of high-temperature and high-pressure reservoir o ffshore.In this paper,the structure of a block of tight gas reservoir was firstly understood,and the reservoir characteristics,fluid characteristics and completion test of exploration wells were analyzed.In this process,the problems to be considered in the development of the new ultra-high density test liquid system are summarized,and the research on its temperature resistance,inhibition,corrosion resistance and reservoir protection performance is focused on.The test liquid base liquid developed in this paper is clean brine.Before the preparation of the new base liquid,the dissolution and compatibility of other commonly used brine are verified.It is clear that it is impossible to increase the density of the tested liquid system by means of brine compounding,which determines the research and development of the new salt-water base liquid.After knowing the basic physical and chemical properties of the new high-density salt-water base liquid,this kind of high-density salt-water base liquid was synthesized in the laboratory,and the temperature resistance experiment,the relationship between mass density and viscosity density and the temperature determination experiment were carried out on the base liquid,and the technology of preparing the new high-density test liquid base liquid was summarized.Experiments show that the test liquid base has a very high density limit(2.8g/cm3)and excellent heat resistance performance(stable performance from 1? to 180?)and good viscosity-temperature performance(shear thinning very well).Then the additives were screened,and the types and appropriate concentrations of the additives,such as viscosifier,corrosion inhibitor,inhibitor and water-release lock agent,were determined,and a set of new ultra-high density non-solid phase test solution technical formula was formed:heteropoly brine+0.5%thiourea+1?2%ZN-5A+1?3%PF-U+7?8%CA101+0.5%JS2.Heteropoly brine test And a series of experiments for test fluid are carried out.The results show that the high density solid free test fluid density can reach up to 2.8g/cm3,its viscosity can be flexibly adjusted and keep at 35mPa's under160?,the cuttings recovery rate reachs to 85%and linear expansion rate is as low as 13%,the corrosion rate for N80 steel is 0.12 mm/a and the test fluid can make core permeability recovery reach above 80%.The test fluid can be well compatible with the field formation water,and the toxicity test indicates that the test fluid is slightly toxic and it can be used in the marine construction environment.