The Prediction Of Lost Circulation Technology Research In Pressure Depleted Formation

Lost circulation is a complex question while drilling fractured formations, and aserious problem restricting the petroleum exploration and development. The prediction oflost circulation technology research in pressure depleted formation aim to study the lostcirculation problem during drilling low pore pressure formation,which has great signif-icance to prevent drilling fluid leakage and other downhole accidents.The pore pressurecoefficient drops after years of development the Yacheng gas field in northern South Chinasea waters,so the lost circulation is very easy to happen when drilling this formation.So theresearches on the mechanism of drilling fluid leakage and the model building of the lostcirculation prediction is significant.This paper surveyed the study of lost circulation in recent years at home and abroadresearch, and summarized the types and the reasons of the drilling fluid leakage and thedrilling fluid leakage mechanism. Based on the relevant knowledge of elastic-plasticmechanics,and established the stress distribution around wellbore and gave the determi-nation method of the relevant rock mechanics parameters. The leakage mechanism can bedivided into fracture leakage, permeability loss and differential pressure loss, according todifferent type of leak and combining the formation damage criterion, leakage pressurecalculating formula are established. In addition to other related pressure was studied, anddeduced the formation collapse pressure, fluctuating pressure and drilling fluid circulatingpressure calculation formula and the security drilling fluid density window.Through the analysis of the dynamic change of all kinds of well logging curve, deter-mined the thief zone. And combining imaging logging and the leak-off velocity todetermine the nature of the loss calculation,which makes the results more accurate under the qualitative and quantitative comprehensive consideration. Then set up a corresponding lossmodel respectively according to the different leakage type and formation damage criterionand programme the well leakage prediction analysis software by using Visual Basic6.0language.And used the software to prove its validity in the area of the south Chinasea,which provided the basis of the determination of drilling fluid density parameters forfield work.