Huaizhong Shi

Hydraulic Pulsed Cavitating Jet-Assisted Drilling

Abstract How to improve drilling rate in deep wells has been a hot subject. Based on modulating pulse jet and cavitating jet, a new drilling tool is designed which couples advantages of both pulse jet and cavitating jet. When drilling fluid flows through the tool during the drilling process, fluid is modulated to pulse and cavitate. Thus, pulse cavitating jet is formed at the outlet of the bit nozzle. Because of jet pulsation, cavitating erosion and local negative pressure affect bottomhole rock. Cleaning and breaking is enhanced and penetration speed is improved. Oil field tests in five wells show good applicability of the tool to bit types, formation, drilling densities, flow rates, and dynamic hydraulic drilling motors, etc. As a result, penetration rates are improved ranging from 10.1 to 31.5%; the maximum working time is about 235.5 hr in downhole. Pulse and cavitating jet coupling will afford an effective means to improve drilling rate for deep wells.

Study and application of a high-pressure water jet multi-functional flow test system

As the exploration and development of oil and gas focus more and more on deeper formation, hydraulic issues such as high-pressure water jet rock breaking, wellbore multiphase flow law, cuttings carrying efficiency, and hydraulic fracturing technique during the drilling and completion process have become the key points. To accomplish related researches, a high-pressure water jet multi-functional flow test system was designed. The following novel researches are carried out: study of high-pressure water jet characteristics under confining pressure, wellbore multiphase flow regime, hydraulic pressure properties of down hole tools during jet fracturing and pulsed cavitation jet drilling, and deflectors friction in radial jet drilling. The validity and feasibility of the experimental results provided by the system with various test modules have proved its importance in the research of the high-pressure water jet and well completion technology.

Design of experimental setup for supercritical CO2 jet under high ambient pressure conditions

With the commercial extraction of hydrocarbons in shale and tight reservoirs, efficient methods are needed to accelerate developing process. Supercritical CO2 (SC-CO2) jet has been considered as a potential way due to its unique fluid properties. In this article, a new setup is designed for laboratory experiment to research the SC-CO2 jets characteristics in different jet temperatures, pressures, standoff distances, ambient pressures, etc. The setup is composed of five modules, including SC-CO2 generation system, pure SC-CO2 jet system, abrasive SC-CO2 jet system, CO2 recovery system, and data acquisition system. Now, a series of rock perforating (or case cutting) experiments have been successfully conducted using the setup about pure and abrasive SC-CO2 jet, and the results have proven the great perforating efficiency of SC-CO2 jet and the applications of this setup.

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.

An experimental system for coiled tubing partial underbalanced drilling (CT-PUBD) technique

To improve the rate of penetration (ROP) in hard formations, a new high-speed drilling technique called Coiled Tubing Partial Underbalanced Drilling (CT-PUBD) is proposed. This method uses a rotary packer to realize an underbalanced condition near the bit by creating a micro-annulus and an overbalanced condition at the main part of the annulus. A new full-scale laboratory experimental system is designed and set up to study the hydraulic characteristics and drilling performance of this method. The system is composed of a drilling system, circulation system, and monitor system, including three key devices, namely, cuttings discharge device, rotary packer, and backflow device. The experimental results showed that the pressure loss increased linearly with the flow rate of the drilling fluid. The high drilling speed of CT-PUBD proved it a better drilling method than the conventional drilling. The experimental system may provide a fundamental basis for the research of CT-PUBD, and the results proved that this new method is feasible in enhancing ROP and guaranteeing the drilling safety.

Properties and testing of a hydraulic pulse jet and its application in offshore drilling

Offshore drilling has attracted more attention than ever before due to the increasing worldwide energy demand especially in China. High cost, long drilling cycles, and low rate of penetration (ROP) represent critical challenges for offshore drilling operations. The hydraulic pulse generator was specifically designed, based on China offshore drilling technologies and parameters, to overcome problems encountered during offshore drilling. Both laboratory and field tests were conducted to collect the characteristics of the hydraulic pulse generator. The relationships between flow rate and pressure amplitude, pressure loss and pulse frequency were obtained, which can be used to optimize operation parameters for hydraulic pulse jet drilling. Meanwhile a bottom hole assembly (BHA) for pulse jet drilling has been designed, combining the hydraulic pulse generator with the conventional BHA, positive displacement motor, and rotary steerable system (RSS) etc. Furthermore, the hydraulic pulse jet technique has been successfully applied in more than 10 offshore wells in China. The depth of the applied wells ranged from 2,000 m to 4,100 m with drilling bit diameters of 311 mm and 216 mm. The field application results showed that hydraulic pulse jet technique was feasible for various bit types and formations, and that ROP could be significantly increased, by more than 25%.

Note: A novel experimental setup for high-pressure abrasive liquid nitrogen jet

A high-pressure abrasive liquid nitrogen (L-N2) jet is considered as an efficient rock-breaking technology due to its unique low-temperature characteristic. In order to experimentally investigate the impact of an abrasive L-N2 jet on rock breakage, a new setup, which considers the low temperature and high expansibility of L-N2, is put forward in this note. The setup is composed of four units: the power system, nitrogen-gas pressurization system, particle mixing system, and impingement system. Both a pre-mixed abrasive L-N2 jet and a post-mixed abrasive L-N2 jet can be achieved by this equipment. Moreover, it can also be used to investigate the influences of injection parameters and particle parameters on rock breakage. A series of experiments have been carried out based on the setup. The results further promote the application of an abrasive L-N2 jet.

Study of the bottom-hole rock stress field under water jet impact

ABSTRACT On the basis of analysis of the bottom-hole rock stress field under water jet impact, there are three types of coupling, which include the coupling of pore fluid and water jet, the coupling of pore fluid and rock matrix, and the coupling of water jet and rock matrix. The fluid-solid coupling model with the four main factors of three-dimensional in-situ stress, fluid column pressure, pore pressure, and water jet velocity is established and calculated by the finite element method and the finite volume method. The results show that the maximum principal stress of the bottom-hole increases with the increase of bottom-hole differential pressure. The maximum jet impact force is proportional to the square of the jet velocity; the pore pressures on the impact surface and along impact axis decrease in the form of cubic parabola with the increase of the distance. The local effect is obvious under water jet impact; the main affected area of the water jet is 2 times jet radius on the impact surface and 2.5 to 3.5 times jet radius along the impact axis when water jet velocity increases from 50 to 250 m/s, which is consistent with the stress wave attenuation theory. Study of the bottom-hole rock stress field under water jet impact provides a numerical research method for study of the water jet rock breaking mechanism under actual drilling conditions and the theoretical basis for faster and more efficient drilling.

Wellbore Flow and Heat Transfer of Drilling with Foam

Abstract On the basis of special physical properties of foam drilling fluid, a mathematical model of foam flow and heat transfer in a wellbore was established, and the solution of the model was proposed. Employing the established mathematical model and its solution, numerical calculation was conducted to analyze the effect of wellbore heat transfer on the hydraulic parameters of foam drilling. The results indicated that foam temperature in a drilling pipe was always lower than that in the annulus and formation temperature. At the bottom of the annulus, foam temperature was lower than the formation temperature, whereas in the top of the annulus, foam temperature was higher than the formation temperature. Most important, with increasing well depth, liquid injection rate, and gas injection rate, the deviation between foam temperature at the bottom of the annulus and formation temperature increased. Wellbore heat transfer not only resulted in increased foam quality in the top of the annulus, bottom pressure, and minimum gas injection rate but also a decrease in the foam quality at the bottom of the annulus and minimum cutting transport velocity. Therefore, the stability and cutting transport capacity of foam decreased. In addition, foam density and Fanning friction coefficient were affected by wellbore heat transfer. Although to a certain extent wellbore heat transfer has an effect on hydraulic parameters of foam drilling, the effect was limited and could be counteracted by increasing gas injection rate and back pressure.

A Numerical Simulation on Characteristics of Annular Helical Flow in Horizontal Wellbore Cleanout

Abstract Trajectories of directional jets and characteristics of annular helical flow in horizontal wellbore cleanout were investigated by the computational fluid dynamics method. For an annular helical flow, the drive source is the partial lateral jets, while the forward and backward jets provide the fluid source. The axial and radial distributions of annular and tangential velocity were analyzed comprehensively. As the distance increases and the flow rate decreases, the strength of the helical flow weakens dramatically. As the rotating speed of the jetter increases, the helical strength enhances slightly. The best performance to achieve annular helical flow is water, followed by Guar-B and Guar-A. This article is beneficial to study the solid transportation in helical flow and optimize the operation parameters.