The SINOPEC Fuling shale gas field is the first large-scale commercial development shale gas field of China, which have been built as a productivity of 5 billion shale gas field until 2015. The problems faced in this location is narrow margin between pore (or collapse)and fracture pressure, therefore the mud loss, collapsing and gas kick are very common problem encountered while drilling, the ROP decreases greatly and the cost of drilling operation increases rapidly. With falling oil and natural gas prices, greater efficiency and excellence in well construction is called for, the MPD related theoretical model and successful use of MPD techniques for improving ROP, controlling gas kick and mud loss, reducing drilling cost for the shale gas horizontal well drilling in Fuling is described. Firstly, a new utility gas kick detect method based on real-time WHP analysis through the theoretical and model analysis was established, in which the WHP variation caused by the tripping, ROP and flow rate variation were taken into account, through which the gas kick can accurately detected as soon as quickly. Secondly, for improving the pressure control precision, a three-layer feedback control method was established and programmed in the controller, through which the bottom hole pressure (BHP) can be adjusted very stable. Moreover, integrated software that combined MPD design and gas kick control simulation was developed based on which the best pressure control procedure and kick initial response can be obtained easily. The MPD technique has been applied in several wells in Fuling shale gas field of SINOPEC, based on the integrated software, the BHP, flow rate, WHP, mud density, and others drilling parameters were all obtained. And through MPD, the drilling results show that the ROP of there wells were improved about 13.9-82%, the outage time have reduced more than 60%. Moreover, through using the low-density drilling mud, the mud loss has been successfully prevented, and also reduced the mud cost. This study will presented the utility theoretical model for MPD gas kick detection, three-layer feedback pressure control method, and the MPD application in shale gas drilling. Through the application of the MPD, the results show that the ROP in shale gas horizontal well drilling has been improved obviously, the optimal oil based drilling mud density was designed has successfully prevented the mud loss and reduced the drilling cost.
Tremendous amounts of hydrocarbons are located in deeper formations, such as in Tarim basin of China, some reservoirs buried so deeply (>7600m) that we experience higher temperature (>180°C) and pressure (>180MPa). And the drilling fluids rheological properties are often affected by HTHP, the careful research on the drilling fluids rheological properties at HTHP is very important for precisely predicting ECD as well as controlling the bottomhole pressure. An accurate prediction methodology of HTHP drilling fluids rheological properties was formulated, which can accurately predict the HTHP rheological parameters. First, the rheological properties of a high density (2.04sg) oil-based drilling fluid at high temperature and pressure were measured. The experimental results indicate that the pressure effect on the rheological properties at ambient temperature was considerable, and this effect could be gradually reduced with the increase of temperature. Second, based on the experimental results, a comprehensive prediction model of HTHP rheological parameters was established, a novel mathematical model for calculating the HTHP shear stress of different shear rate was formulated, the influence of high temperature was taken into account first and then the comprehensive influence of high temperature and high pressure was taken into account too. Based on the mathematical model, we can obtain the HTHP shear stress of different shear rate easily. Based on the HTHP shear stress, a utility HTHP rheological model optimization method and parameters calculation model was proposed. Because of this model related the HTHP shear stress to the influence of HTHP directly, and then calculated the rheological parameters, rather than relating the specific rheological parameters to HTHP as the traditional models, therefore the prediction model is applicable for all rheological model (Bingham, Power-Law, Herschel-Bulkely, Robertson-Stiff et al.). Finally, a novel HTHP rheological properties analyzing system was developed, through which the HTHP rheological parameters can be obtained easily, a series predictions of this model have been compared with the experimental data about different type drilling fluids (oil-based, synthetic-based fluids), and the results show very good agreements with the experimental data. Therefore it can be used to accurately predict the rheological parameters and calculate the hydraulic parameters in the HTHP conditions while drilling.
Drilling wells for oil/gas has been increasingly challenging with the companies moving towards difficult environments, such as in Tarim basin of China, some reservoirs buried so deeply (>7,000m) that we experience high temperature and pressure. The problems faced in these locations range from very narrow margin between pore (or collapse) and fracture pressure. The density of drilling fluid is often affected by HTHP, the careful research on the drilling fluids density at HTHP is very important for precisely predicting ESD as well as controlling the downhole pressure. A utility calculation model of drilling fluids density and ESD was proposed, which can predict the HTHP density and ESD. Firstly, a new utility artificial neural network HTHP drilling fluid density prediction model was established based on the traditional BP neural network and PSO (Particle Swarm Optimization) optimization method. Then PSO-BP neural network HTHP drilling fluid density prediction model was proposed, in which the influence of drilling fluid component (oil phase, water phase volume fraction) was taken into account. Available experimental measurements of water-based and oil-based drilling fluids at pressure ranging from 0-96MPa and temperatures up to 183°C were used to develop and the PSO-BP network model and then the network weights, threshold parameters. Through this model the high-precision HTHP drilling fluids density can be obtained easily with the knowledge of the drilling fluids component data (oil phase and water phase volume fractions) and its density at standard conditions(0MPa, 20°C) based on the basic principle of PSO-BP network. Moreover, an new comprehensive ESD calculation model of HTHP well was established, which is applicable for all common type drilling fluids and through we can obtained the ESD profile of the well easily. The prediction of this model has been compared with an extensive set of data from literature, the comparisons of different fluids density in HTHP show very good agreement, the prediction accuracy was improved, and in which the maximum average absolute error of predictions is less than 0.005sg. Finally, the proposed model has been applied for HTHP drilling fluids density and ESD prediction in several wells of the Tarim basin in China, the results show that the proposed model can exactly provide the HTHP drilling fluids density and ESD profile. This study proposed an utility calculation of HTHP drilling fluids density and ESD profile while drilling, based on the new PSO-BP neural network, the optimal network weights, threshold parameters of was obtained, through which the high-precision drilling fluids density and ESD can be obtained easily. Moreover, the model has been verified and applied for field monitoring. Therefore, this model can be applied to provide more accurate predictions of HTHP drilling fluids density and ESD while drilling.
Similar materials of surrounding rock are used to simulate the rock mass in the geomechanical model test. The discrete element method has the advantage of simulating the behavior of fractures between particles at the micro-scale, which can further reveal the failure mechanism of surrounding rock in combination with the model test. However, microparameters need to be calibrated before the simulation. In this paper, three kinds of bond models are described, and their application is analyzed. The soft-bond model is determined as the constitutive model of particles' contacts. Then, the simulation method of the biaxial test is introduced in detail, and the simulation results of the rigid-wall and flexible-wall methods are compared. Furthermore, based on the control variable method, a large number of biaxial tests are carried out by the rigid-wall method. Through single-factor sensitivity analysis and multi-factor variance analysis, the qualitative relationship between macro- and micro-parameters and the significant influencing factors of each macro-parameter are obtained. On this basis, the multivariate nonlinear multi-scale mathematical model is established by regression analysis. The appropriate micro-parameters are obtained by solving the proposed mathematical model using three optimization methods combined with the results of laboratory test measurements. This entire process constitutes the calibration method proposed in this paper. The reliability of the calibration method in this paper is verified by comparing the calculated macro-parameters, stress-strain curves, and failure modes with those of laboratory tests.
Managed pressure drilling (MPD) technique can stop and remove a kick without shut-in procedure while keeping the bottomhole pressure relatively constant while a kick was detected. But the key for a successful kick removal operation depend on accurate, real-time knowledge of wellbore hydraulics. Therefore, the transient multiphase flow calculation for MPD kick control should be developed for obtaining high-precision hydraulics. Firstly, a real-time multiphase hydrodynamic model for kick control of MPD was proposed, in which the gas solubility in drilling fluids is take into account. Because of the well head pressure need to adjust in real-time during MPD, therefore the influence caused by real-time adjusting of WHP for gas migration and phase change was take into account too. And as a consequence there are more boundary conditions and dynamic parameters of this model than the traditional multiphase model. Secondly, the finite difference method was used to solve the proposed model, and then a comprehensive solution procedure is proposed, in which the different boundary conditional mode of MPD is considered, based on which the numerical solution of kick control for different MPD mode can be obtained easily. Moreover, a series of system calculation software were developed to predicted pit gain, flow patterns, circulating pressures, gas top, bottomhole hydraulics and the related control parameters for control the kick while MPD. The proposed model has been verified with experimental data collected from scientific experimental well of SINOPEC, there is an excellent match between the calculated and measured data and the calculation accuracy is higher than 95%. Furthermore, this calculation software has been used for analyzing the MPD kick control during drilling shale gas horizontal wells of SINOPEC, and it runs smoothly with convenient operation. Therefore it can be seen this system can be applied to provide more convenient fast and precise dynamic parameters monitoring for control kick while MPD. This paper established a novel real-time multiphase hydrodynamic model and a systematic calculate software, which has been verified with experimental data and applied in shale gas field. Through the field application, the results show that it can provide more accurate prediction of wellbore multiphase flow parameters. Therefore it can be seen that this novel method can be applied for MPD kick control to provide more precise dynamic parameters for kick control while MPD.
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