Analysis of the Lost Circulation Problem

The well-known“lost circulation”problem refers to the uncontrolled flow of whole mud into a formation.In order to address the problem related to the paucity of available data,in the present study,a model is introduced for the lost-circulation risk sample profile of a drilled well.The model is built taking into account effective data(the Block L).Then,using a three-dimensional geological modeling software,relying on the variation function and sequential Gaussian simulation method,a three-dimensional block lost-circulation risk model is introduced able to provide relevant information for regional analyses.

Uncertainty Analysis of the Residual Strength of Non-Uniformly Loaded Casingsin Deep Wells

An uncertainty analysis method is proposed for the assessment of the residual strength of a casing subjected to wear and non-uniform load in a deep well.The influence of casing residual stress,out-of-roundness and non-uniform load is considered.The distribution of multi-source parameters related to the residual anti extrusion strength and residual anti internal pressure strength of the casing after wear are determined using the probability theory.Considering the technical casing of X101 well in Xinjiang Oilfield as an example,it is shown that the randomness of casing wear depth,formation elastic modulus and formation Poisson’s ratio are the main factors that affect the uncertainty of residual strength.The wider the confidence interval is,the greater the uncertainty range is.Compared with the calculations resulting from the proposed uncertainty analysis method,the residual strength obtained by means of traditional single value calculation method is either larger or smaller,which leads to the conclusion that the residual strength should be considered in terms of a range of probabilities rather than a single value.

Numerical Analysis of Residual Strength in the Perforated Casing of Ultra Deep Wells

A three-dimensional model for the numerical simulation of casing-cement behavior is used to investigate residual strength in the perforated casing of ultra deep wells.The influence of the hole diameter,hole density and phase angle on the residual strength of the casing under non-uniform stress and fracturing conditions is revealed through the consideration of different perforation parameters.It is shown that the residual strength of the casing increases with the hole diameter and periodically changes with the hole density;the phase angle is the main factor that affects the residual strength of the perforated casing,and the perforation should be avoided in the direction of the minimum principal stress to reduce stress concentration at the perforation hole.Moreover,as shown by a companion orthogonal experiment,the descending order of influence of the different influential parameters is:phase angle,hole diameter,hole density and the thickness of casing.

Analysis of the Applicability of a Risk Quantitative Evaluation Method to High Temperature-Pressure Drilling Engineering

The optimization of methods for the quantitative evaluation of risks in drilling engineering is an effective means to ensure safety in situations where high temperature and high pressure blocks are considered.In such a context,this study analyzes the complexity of the drilled wells in such blocks.It is shown that phenomena such as well kick,loss,circulation,and sticking,are related to the imbalance of wellbore pressure.A method for risk quantitative evaluation is proposed accordingly.The method is used to evaluate the risk for 9 drilled wells.By comparing the predictions of the method with actual historical data related to these wells,it is found that the coincidence rate is about 95%.

Analysis of Multiple Annular Pressure in Gas Storage Well and High-Pressure Gas Well

In gas storage or high-pressure gas wells,annular pressure is an unavoidable threat to safe,long-term resource production.The more complex situation,however,is multiple annular pressure,which means annular pressure happens in not only one annulus but two or more.Such a situation brings serious challenges to the identification of well integrity.However,few researches analyze the phenomenon of multiple annular pressure.Therefore,this paper studies the mechanism of multi-annular pressure to provide a foundation for its prevention and diagnosis.Firstly,the multi-annular pressure is classified according to the mechanism and field data.Then the failure mechanism and function of the wellbore safety barriers in the process of passage formation are analyzed.Finally,some suggestions are put forward for identifying and controlling multi-annular pressure.The results show that gas storage wells and high-pressure gas wells have the conditions to generate pressure channels,which leads to the expansion of annular pressure from a single annulus to multiple annuli.The pressure channel is composed of the tubing string,casing string,and a cement mantle,and the failures among the three have causal and hierarchical relationships.According to the channel direction,it can be divided into two types:tubing-casing annulus to casing annulus and casing annulus to the tubing-casing annulus,of which the former is more harmful.Some measures can be considered to prevent pressure channeling,including improvement of cementing quality,revision of maximum allowable annular pressure,and suitable frequency of pressure relief.

Comparison of survival prediction values of different scoring models for patients undergoing transjugular intrahepatic portal shunt:A multicenter retrospective study

Aim:The aim of this study is to compare the prognostic values of the Child–Pugh,integrated model for end‐stage liver disease(iMELD),albumin–bilirubin(ALBI),and Freiburg index of postsurvival(FIPS)scores in patients undergoing transjugular intrahepatic portosystemic shunt(TIPS).Methods:We conducted a multicenter retrospective study including patients who underwent TIPS by collecting data from several hospitals in southwest China between January 2014 and February 2021.We compared the performance of different scoring models for survival prediction in these patients.The performance of each scoring model was assessed via area under the receiver‐operating characteristic(AUROC)curve analysis.Results:The study included 378 TIPS patients(268 men,110 women;median age 52[interquartile range,45–60]years).Age;cirrhosis etiology;ascites severity;albumin levels;international normalized ratio;total bilirubin levels;sodium levels;and Child–Pugh,iMELD,ALBI,and FIPS scores were significant prognostic factors in cirrhotic patients who underwent TIPS.The Child–Pugh,iMELD,ALBI,and FIPS scores were all independent predictors of survival in TIPS patients.Survival analysis showed that all scoring models effectively stratified the prognostic risk of these patients.The Child–Pugh score was the best predictor of postoperative survival,followed by the ALBI and FIPS scores.The iMELD score was the worst predictor.The Child–Pugh,iMELD,ALBI,and FIPS scores predicted the 1‐year postoperative survival,with AUROC values of 0.832,0.677,0.761,and 0.745,respectively,and the 3‐year postoperative survival,with AUROC values of 0.710,0.668,0.721,and 0.658,respectively.The calibration curve showed that the Child–Pugh,ALBI,and FIPS models performed well in predicting 1‐and 3‐year survival,whereas the iMELD model was a poor predictor.Conclusions:The four scoring models can predict survival in cirrhotic patients after TIPS and can effectively stratify prognostic risk.The Child–Pugh score may be more suitable for predicting survival after TIPS in patients with liver cirrhosis.