We have integrated rock mechanics and acoustic experiments, full-wave array acoustic testing, formation microscanner image logging, and hydraulic fracturing data to evaluate the coupling relationship between current in-situ stress and natural fractures. We used the data of the Yanchang Formation in the DL block of the western Ordos Basin, China, as an example. Our results find that the Yanchang Formation mainly develops high-angle fractures and vertical fractures. Furthermore, the in-situ stress state of the target sandstone strata satisfies σv> σH> σh. Nearly vertical and high-angle fractures are formed in the environment when σv is the maximum principal stress. Therefore, the current in-situ stress state of the target layer matches the induced fractures (longitudinal tensile-induced fractures) and natural fractures. As the buried depth increases, the difference between the horizontal maximum and minimum stresses ( σH- σh) has a tendency to first decrease and then increase, and its conversion depth is approximately 2000 m. Natural fractures are not developed in the distributary bay (the lowest horizontal stress area) and the thick sand area in the middle of the main river channel (the largest horizontal stress area). Natural fractures are mainly developed on the two wings of the main channel, and their horizontal stress is approximately 2–4 MPa lower than the central part of the main channel. We determined a correlation between fractures and sedimentary facies, and we have an important reference value for improving the drilling success rate of tight oil reservoirs. Furthermore, our study provides insights into the prediction of fractures and sweet spots for further exploration and hydraulic fracturing activities in the studied area and elsewhere in continental tight sandstone reservoirs.

Coupling relationship between current in-situ stress and natural fractures of continental tight sandstone oil reservoirs

The utility model relates to a double-pulse hydraulic oscillator for well drilling and belongs to the technical field of petroleum and natural gas exploitation and well drilling tools. The double-pulse hydraulic oscillator for well drilling is composed of an oscillation short section assembly and a power short section assembly, and is characterized in that the oscillation short section assembly is composed of a spline spindle, a connection sleeve, a pressure transducer, an oscillation shell and the like; the power short section assembly comprises a compression sleeve and a turbine shaft; a sealing part is installed between the spline spindle and the connection sleeve; the connection sleeve is connected with the oscillation shell; the lower end of the oscillation shell is connected with the power short section assembly; the compression sleeve at the upper end of the power short section assembly is connected with the oscillation shell; the lower end of the compression sleeve is connected with a power shell; the turbine shaft is installed in the center of the power shell; the turbine shaft is provided with an alignment bearing, a turbine stator, a turbine rotor, two sets of movable valves and fixed valves, a sleeve, a shunt ring, a shunt sleeve and a thrust bearing sequentially from top to bottom. No radial swing exists, large axial oscillation with high frequency can be achieved under small flow, friction resistance is small, the drilling pressure is effectively increased, and the mechanical drilling speed is increased.

Double-pulse hydraulic oscillator for well drilling

The existing artificial intelligence model uses single-point logging data as the eigenvalue to predict shear wave travel times (DTS), which does not consider the longitudinal continuity of logging data along the reservoir and lacks the multiwell data processing method. Low prediction accuracy of shear wave travel time affects the accuracy of elastic parameters and results in inaccurate sand production prediction. This paper establishes the shear wave prediction model based on the standardization, normalization, and depth correction of conventional logging data with five artificial intelligence methods (linear regression, random forest, support vector regression, XGBoost, and ANN). The adjacent data points in depth are used as machine learning eigenvalues to improve the practicability of interwell and the accuracy of single-well prediction. The results show that the model built with XGBoost using five points outperforms other models in predicting. The R2 of 0.994 and 0.964 are obtained for the training set and testing set, respectively. Every model considering reservoir vertical geological continuity predicts test set DTS with higher accuracy than single-point prediction. The developed model provides a tool to determine geomechanical parameters and give a preliminary suggestion on the possibility of sand production where shear wave travel times are not available. The implementation of the model provides an economic and reliable alternative for the oil and gas industry.

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Artificial Intelligence Method for Shear Wave Travel Time Prediction considering Reservoir Geological Continuity


 Large numbers of deep-water drilling practices have shown that more than 60% of deep-water wells have complex leak-off during the drilling process, which poses great difficulties and challenges for the safety and operation time of deep-water drilling. The purpose of this article is to establish a method for predicting the fracture pressure in shallow formations. In this study, the deep-water shallow formation was divided into the upper unconsolidated soil layer, and the lower diagenetic rock layer according to the geotechnical distribution characteristics of the deep-water shallow formation. The location of the transition soil/rock layer zone was determined using the upper soil layer density trend line, and the lower rock layer density log data regression trend line. The deep-water shallow fracture pressure prediction model was established based on the soil/rock transition zone. The shear failure criterion was used above the transition zone, and the tensile failure criterion is used below the transition zone. The shallow fracture pressure of six drilled exploratory wells in the X block from the South China Sea was calculated using this new method and the calculation errors were all less than 3.18%. Moreover, the shallow fracture pressure body in this block was established using the Kriging interpolation method based on six drilled exploratory wells data. This shallow fracture pressure body established here was used to predict nine development wells shallow fracture pressure with a predictive error of less than 1.7% and there were no drilling accidents. The case study demonstrates that the new model can significantly improve the prediction accuracy has good prospects for popularization and application.

A Novel Method for Fracture Pressure Prediction in Shallow Formation During Deep-Water Drilling

Cement erosion process with recyclable sand particle water-jet impacts

The longitudinal vibration of the drill pipe contains considerable energy which can be used to improve the rock-breaking efficiency during drilling. It is very important to the development of drilling speed-up tools to have a comprehensive understanding of the energy conversion efficiency of downhole drill string vibration. In this paper, the characteristics of downhole bit load and longitudinal vibration of drill string under different conditions were studied in the experiment, and the analysis method of energy conversion efficiency from drill string vibration to spring potential energy was proposed. The experimental analysis showed that the fluctuation of the downhole bit load was reduced by 10%–90% after the spring was installed in the bottom hole assembly. The rotation rate and the spring elastic stiffness had a significant and positive influence on the fluctuation amplitude of the downhole bit load. Meanwhile, the longitudinal vibration amplitude and acceleration of the drill string peaked at the elastic stiffness of 1 kN/mm. The closer the spring position to the drill bit was, the more severe the longitudinal vibration of the drill string above the spring component was. The bit load and the rotation rate had a positive influence on the severity of longitudinal vibration. The analysis of energy conversion efficiency showed that the available mechanical energy range of the longitudinal vibration of the drill pipe was about 200–420 kW. The work power of the drill string vibration to the spring component increased sharply and then decreased with the increasing of elastic stiffness. The energy conversion efficiency came to the optimal value when the elastic stiffness was between 1 kN/mm and 2 kN/mm. Increasing the rotation rate, keeping the bit load below 134.5 kN and installing the spring component near the drill bit are beneficial for improving the energy conversion efficiency of drill string vibration. This paper reveals the main factors affecting the energy conversion efficiency of drill string vibration and their influencing laws, and determines the range of WOB, rotation speed, spring position and stiffness to obtain the best energy conversion efficiency.

Dynamic Characteristics of Downhole Bit Load and Analysis of Conversion Efficiency of Drill String Vibration Energy

The invention belongs to the deepwater oil gas drilling well field, and specifically relates to a deepwater drilling well gas cut monitoring method based on marine riser gas-liquid two-phase flow identification; the method comprises the following steps: arranging ultrasonic transducers in contrapositions on bottom of the marine riser so as to monitor gas cut signals; according to a set quantification corresponding relation between sound wave signal attenuation and cross section gas contain rate, combining a deepwater drilling well shaft gas liquid two-phase flow model and a credibility containing stratum pressure prediction method so as to set up a shaft gas cut level inverse computation method based on marine riser gas cut monitoring data, thus spotting gas cut in advance, realizing real time quantification description of the shaft gas cut condition, and forming the deepwater drilling well gas cut monitoring method based on marine riser gas-liquid two-phase flow identification. The method can measure more real data, can fully reflect the cross section gas containing rate, and can correct bottom hole prediction originality pressure according to marine riser sound wave monitoring data, so the shaft gas cut level inverse computation result can be more closer to real conditions, and reasonable measurement can be taken to control gas cut.

Deepwater drilling well gas cut monitoring method based on marine riser gas-liquid two-phase flow identification

The invention relates to a pulse impact producing mechanism and a center differential pressure drill comprising the same. The pulse impact producing mechanism comprises a righting element, a driving element, a rotating element and a throttling element which are placed sequentially, the righting element, the driving element and the rotating element are connected sequentially, the throttling element and the rotating element are in clearance fit, overcurrent channels which are used for flowing of a drilling fluid are arranged on the righting element and the throttling element, the driving element drives the rotating element to rotate, and the overcurrent channels on the rotating element and the throttling element move relatively. The center differential pressure drill comprises a reaming bit, the pulse impact producing mechanism, a pressure regulating element, a transmission mechanism and a pilot bit, and the pressure regulating element, the transmission mechanism and the pilot bit are connected sequentially. Compared with the prior art, the cuttings hold-down effect of the pilot bit and the reaming bit is reduced while rotary impact drilling of the pilot bit can be realized, further the purposes of protecting the bits, prolonging the service lives and improving the drilling speed are realized, and the drilling effect is further improved.

Pulse impact producing mechanism and center differential pressure drill comprising same

The RSS has been widely used in directional drilling. In order to enhance wellpath control accuracy and efficiency of the static push-the-bit RSS, a powerful BUR prediction method is reconstructed by coupling a rotary steerable bottom-hole assembly (RSBHA) mechanical model and a drill bit–rock interaction model. This article showed that when establishing the RSBHA mechanical model by using the continuous beam column method, the steering rib should be treated as an eccentric stabilizer to consider the contact effect between the steering rib and wellbore wall. For the beam column containing the flexible sub and between two stabilizers, it should be rearranged into three beam columns, and the lower and upper steps of the flexible sub should be considered as virtual supports. The equilibrium tendency method (ETM) to predict the BUR can enhance wellpath prediction accuracy than those of traditional methods. Under 3D conditions, the total drilling tendency angle should be denoted by inclination tendency angle and azimuth tendency angle to enhance the solution efficiency. Case analyses have verified that the average forecast error of the BUR prediction model in this article is less than 1°/30 m.

A Powerful Build-Up Rate (BUR) Prediction Method for the Static Push-the-Bit Rotary Steerable System (RSS)

The utility model relates to underground equipment for oil gas drilling, in particular to an underground check valve for oil gas drilling. The technical scheme is as follows: the underground check valve mainly consists of a valve body, a valve core pressing sleeve, a sealing assembly, a valve core, a return spring and a valve seat, wherein the top and bottom of the valve body are both provided with a connection thread; the outer side of the valve core pressing sleeve is of a trapezoidal thread structure, a runner and a center hole are arranged at the middle of the valve core pressing sleeve, and the valve core pressing sleeve is mounted at the top end of the valve body; the sealing assembly is compacted and positioned in the valve body by the valve core pressing sleeve and matched with the valve core; the valve seat is mounted at the bottom of an inner cavity of the valve body; and the return spring is arranged at the bottom of the valve core and mounted between the valve seat and the valve core. The underground check valve provided by the utility model has the beneficial effects that the return spring is away from a channel of high-speed flowing drilling fluid, and the limiting of the valve core is realized through the match between the upper step surface of the valve seat and the lower step surface of the valve core, thus the overpressure damage of the return spring is prevented, and the working life of the easily-damaged return spring is effectively prolonged.

Yuqiang Xu

Papers

Dynamic Characteristics of Downhole Bit Load and Analysis of Conversion Efficiency of Drill String Vibration Energy

Deepwater drilling well gas cut monitoring method based on marine riser gas-liquid two-phase flow identification

Pulse impact producing mechanism and center differential pressure drill comprising same

A Powerful Build-Up Rate (BUR) Prediction Method for the Static Push-the-Bit Rotary Steerable System (RSS)

Underground check valve for oil gas drilling