Shouceng Tian

Flow field simulation of supercritical carbon dioxide jet: Comparison and sensitivity analysis

As a new jet technology developed in recent years, the supercritical carbon dioxide (SC-CO2) jet technology enjoys many advantages when applied in oil and gas explorations. In order to study the properties and parametric influences of the SC-CO2 jet, the flow fields of the SC-CO2 jet are simulated using the computational fluid dynamics method. The flow field of the SC-CO2 is compared with that of the water jet. The influences of several parameters on the flow field of the SC-CO2 jet are studied. It is indicated that like the water jet, the velocity and the pressure of the SC-CO2 jet could be converted to each other, and the SC-CO2 jet can generate a significant impact pressure on the wall, the SC-CO2 jet has a stronger impact pressure and a higher velocity than those of the water jet under the same conditions, the maximum velocity and the impact pressure of the SC-CO2 jet increase with the increase of the nozzle pressure drop, under the stimulation condition of this study, the influence of the SC-CO2 temperature on the impact pressure can be neglected in engineering applications, while the maximum velocity of the SC-CO2 jet increases with the increase of the fluid temperature. This paper theoretically explores the properties of the SC-CO2 jet flow field, and the results might provide a theoretical basis for the application of the SC-CO2 jet in oil and gas well drillings and fracturing stimulations.

A FRACTAL PERMEABILITY MODEL FOR SHALE MATRIX WITH MULTI-SCALE POROUS STRUCTURE

Nanopore structure and its multiscale feature significantly affect the shale-gas permeability. This paper employs fractal theory to build a shale-gas permeability model, particularly considering the effects of multiscale flow within a multiscale pore space. Contrary to previous studies which assume a bundle of capillary tubes with equal size, in this research, this model reflects various flow regimes that occur in multiscale pores and takes the measured pore-size distribution into account. The flow regime within different scales is individually determined by the Knudsen number. The gas permeability is an integral value of individual permeabilities contributed from pores of different scales. Through comparing the results of five shale samples, it is confirmed that the gas permeability varies with the pore-size distribution of the samples, even though their intrinsic permeabilities are the same. Due to consideration of multiscale flow, the change of gas permeability with pore pressure becomes more complex. Consequently, it is necessary to cover the effects of multiscale flow while determining shale-gas permeability.

Investigation and Application for Multistage Hydrajet-Fracturing with Coiled Tubing

Abstract Continuing high prices for oil and gas stimulate new technologies improve the production of low permeability reservoirs. Hydrajet-fracturing with coiled tubing, a unique technology for low-permeability horizontal and vertical wells, uses fluids under high pressure to initiate and accurately place a hydraulic fracture without packer, saving operating time and lowering operating risk. The mechanisms of hydrajet-perforation and hydrajet-fracture initiation are studied in this article. Frictions for one kind of fracturing fluid in coiled tubing have been computed to determine pump pressure and flow rate for field testing. Tools for hydrajet fracturing are designed as well. The first successful field testing in China of multistage hydrajet-fracturing using coiled tubing has proven that the theoretical calculation and field-testing data of hydraulic parameters are basically identical. It has also proven that tools meet the requirement of field testing.

Multistage hydraulic jet acid fracturing technique for horizontal wells

Abstract Acid fracturing in deep carbonate reservoirs is challenged by deep well stimulation with high temperature (>120 °C), high fracture pressure (>2.0 MPa/m), high flow friction, and strong reservoir heterogeneity. To meet these challenges, a new stimulation method, called the hydraulic jet acid fracturing technique, was developed. According to the mechanisms of hydraulic jet acid fracturing, the authors self-design the downhole injector and pipe strings used in multistage hydraulic jet acid fracturing and provide optimization standards for the nozzle number and diameter combination, abrasive perforating parameter, and pumping program. The technique realizes multistage acid fracturing by hydraulic separation and features simple downhole tools, high temperature resistance (160 °C), low cost and risk. In addition, hydraulic acid injection can extend effective acid corrosion distance nearby well and enhance the acidification effect. The optimal jet phasing is 60 degrees with spiral arrangement to lower formation fracture pressure. A relationship chart between optimal flow rate and wellhead pressure is established, which helps to increase flow rate as far as possible under wellhead assembly capacity and to determine nozzle diameter and number. Results from field tests show that this method can work at a maximum depth of 6 400.53 m, with a total acid volume of up to 618 m3. It is effective in creating acid fractures in ultra-deep horizontal wells.

Numerical simulation of the abrasive supercritical carbon dioxide jet: The flow field and the influencing factors

The supercritical carbon dioxide (SC-CO2) jet can break rocks at higher penetration rates and lower threshold pressures than the water jet. The abrasive SC-CO2 jet, formed by adding solid particles into the SC-CO2 jet, is expected to achieve higher operation efficiency in eroding hard rocks and cutting metals. With the computational fluid dynamics numerical simulation method, the characteristics of the flow field of the abrasive SC-CO2 jet are analyzed, as well as the main influencing factors. Results show that the two-phase axial velocities of the abrasive SC-CO2 jet is much higher than those of the abrasive water jet, when the pressure difference across the jet nozzle is held constant at 20 MPa, the optimal standoff distance for the largest particle impact velocity is approximately 5 times of the jet nozzle diameter; the fluid temperature and the volume concentration of the abrasive particles have modest influences on the two-phase velocities, the ambient pressure has a negligible influence when the pressure difference is held constant. Therefore the abrasive SC-CO2 jet is expected to assure more effective erosion and cutting performance. This work can provide guidance for subsequent lab experiments and promote practical applications.

Mechanism and Characteristics of Horizontal-Wellbore Cleanout by Annular Helical Flow

In addition, an experiment of horizontal wellbore cleanout was carried out to study the sand bed suspension efficiency in stationary circulation stage and wiper trip stage. There exists a critical length between sand bed and cleaning tool which lead to different mechanisms to transport the sand. In this study, the critical length increases rapidly with the increase of flow rate, tubing size and sand size.

The Boosting Mechanism and Effects in Cavity During Hydrajet Fracturing Process

Abstract This article presents the boosting mechanism in cavity during a hydrajet fracturing process. It is found that there are two kinds of pressures enhancing the value within a cavity. One is the impact pressure by the jetted fluid from a nozzle, and the other is back-pressure by the hole in a casing. A numerical simulation method was utilized to evaluate boosting effects combined with experiment results. Distribution of pressure in a cavity was obtained. The results show that the pressure in a cavity is higher than that in the wellbore. It will be increased with the nozzle pressure drop and nozzle diameter rising. The hole plays an important seal role to created back-pressure, which boosts the pressure greatly. The boosting value can reach approximately to 8.2 MPa with Φ 6 mm nozzle diameter and differential pressure of 25 MPa.

New Technique: Hydra-jet Fracturing for Effectiveness of Multi-zone Acid Fracturing on an Ultra Deep Horizontal Well and Case Study

of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of IADC/SPE copyright. Abstract The placement of multiple fractures in deep horizontal wells is more difficult than that in shallow formations due to HTHP conditions. This paper presents the latest advances in hydra-jet acid fracturing for solving problems in the process of deep well acid fracturing. Basic researches and application evaluations were conducted to overcome down-hole conditions. Special schedule was designed delicately to lower the cracking pressure. The jet velocity was increased more than 800ft/sec to enhance the penetration efficiency. Acid pad fluid also was jetted to the target point for 15 minutes to erode carbonate rock, which leads to lower the rock strength. An explanation how to execute process has been included in details. The different procedures of treatment in shallow and deep reservoir were also discussed.

A Theoretical Analysis of Pore Size Distribution Effects on Shale Apparent Permeability

Apparent permeability is an important input parameter in the simulation of shale gas production. Most apparent permeability models assume a single pore size. In this study, we develop a theoretical model for quantifying the effect of pore size distribution on shale apparent permeability. The model accounts for the nonuniform distribution of pore sizes, the rarefaction effect, and gas characteristics. The model is validated against available experimental data. Theoretical calculations show that the larger the pore radius, the larger the apparent permeability. Moreover, the apparent permeability increases with an increase in the width of pore size distribution, with this effect being much more pronounced at low pressure than at high pressure.

A Study on the Effect of Bottom-hole Differential Pressure on the Rock Stress Field

Bottom-hole differential pressure is one of the most important factors that affects the drilling penetration rate. The purpose of the article is to study the effect of bottom-hole differential pressure on the vertical bottom-hole stress field. On the basis of mechanical analysis of the bottom-hole rock, the fluid-solid coupling model with the bottom-hole differential pressure is established under axisymmetry condition and is solved by using a numerical method. The comparison of the distribution of borehole wall stress between the numerical and theoretical solution is performed to verify the feasibility and rationality of the model. Then analysis of the stress state of the whole bottom-hole rock to break is carried out. The results show that the numerical solution is consistent with the theoretical solution and the fluid-solid coupling model is reasonable. With the increasing of the bottom-hole differential pressure, the bottom-hole tensile stress increases and compressive stress decreases and tensile region becomes larger. The whole bottom-hole rock to break is divided into three regions: triaxial tension region, biaxial compression and unidirectional tension region, and triaxial compression region. Qualitative and quantitative analysis of the bottom-hole stress field under different differential pressure provides the theoretical basis for rock breaking mechanism and faster and more efficient drilling.