Xianzhi Song

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.

Optimization of Operation Parameters for Helical Flow Cleanout with Supercritical CO2 in Horizontal Wells Using Back-Propagation Artificial Neural Network

Sand production and blockage are common during the drilling and production of horizontal oil and gas wells as a result of formation breakdown. The use of high-pressure rotating jets and annular helical flow is an effective way to enhance horizontal wellbore cleanout. In this paper, we propose the idea of using supercritical CO2 (SC-CO2) as washing fluid in water-sensitive formation. SC-CO2 is manifested to be effective in preventing formation damage and enhancing production rate as drilling fluid, which justifies tis potential in wellbore cleanout. In order to investigate the effectiveness of SC-CO2 helical flow cleanout, we perform the numerical study on the annular flow field, which significantly affects sand cleanout efficiency, of SC-CO2 jets in horizontal wellbore. Based on the field data, the geometry model and mathematical models were built. Then a numerical simulation of the annular helical flow field by SC-CO2 jets was accomplished. The influences of several key parameters were investigated, and SC-CO2 jets were compared to conventional water jets. The results show that flow rate, ambient temperature, jet temperature, and nozzle assemblies play the most important roles on wellbore flow field. Once the difference between ambient temperatures and jet temperatures is kept constant, the wellbore velocity distributions will not change. With increasing lateral nozzle size or decreasing rear/forward nozzle size, suspending ability of SC-CO2 flow improves obviously. A back-propagation artificial neural network (BP-ANN) was successfully employed to match the operation parameters and SC-CO2 flow velocities. A comprehensive model was achieved to optimize the operation parameters according to two strategies: cost-saving strategy and local optimal strategy. This paper can help to understand the distinct characteristics of SC-CO2 flow. And it is the first time that the BP-ANN is introduced to analyze the flow field during wellbore cleanout in horizontal wells.

Mechanism and Parameter Optimization of Abrasive Water Jet Perforation

This chapter investigates the mechanisms of abrasive water jet (AWJ) perforation, and the results of laboratory experiments and field cases on abrasive AWJ perforation are presented. AWJ perforation is a two-stage process: the ductile casing erosion stage and the brittle rock penetration stage. Each stage follows different failure mechanisms. Experiments were conducted to reveal the effect of pressure, flow rate, abrasive material, particle size, abrasive concentration, ambient pressure, rock material, exposure time, etc., on penetration performance. The conclusions derived from the laboratory experiments were supported by field tests. Further simulation experiments of AWJ perforation are illustrated in the third section.

Theoretical Basis of Abrasive Jet

Water jet with high pressure can successfully cut rock, steel, and even reinforced concrete. However, at lower pressure, mixing a certain amount of abrasive particles in the water jet can also greatly improve the jet ability and effectively cut materials. High-pressure water jet blended with abrasives is known as an abrasive jet.

Numerical and Experimental Study of Flow Field in a Hydra-Jet Hole

Understanding the characteristics of a flow field in a hydra-jet hole is crucial to explain why hydra-jets can realize pinpoint fracturing without using a mechanical packer. This chapter reports a numerical simulation and experimental study on flow fields in a hydra-jet hole, involving the modeling, experimental setup and scheme, and results. From laboratory experiments and numerical simulation data, five key factors—confining pressure, nozzle pressure drop, nozzle distance, inlet ratio, and perforation tunnel depth—were utilized to preliminarily calculate the law of pressure distribution of a perforation tunnel and the jetting boost pressure. The results indicated that the nozzle pressure drop and entry ratio significantly affect the pressure distribution of the perforation tunnel and the jetting boost pressure and that the nozzle pressure drop is linearly related to the jetting boost pressure.

Chapter Eight – Field Application

This chapter mainly presents the technologies of formation feasibility, operation procedures, bottom-hole assembly damage or failure, possible risks in field performance and the corresponding measures to deal with them, and typical field cases. These contents are summarized according to practical performance. The lessons learned from field operations will be able to provide a valuable reference for potential application. In addition, typical wells are listed to show the feasibility of this technology to different completion categories.

Flow Behavior and Friction Characteristics of Fluid Flow in Coiled Tubing

The coiled tubing (CT) has many applications in the petroleum industry, which include drilling (CT drilling), cementing, wellbore cleanout, acidizing, and hydraulic fracturing. In contrast, the excessive friction pressure loss, due to the relatively small tubing diameter and tubing curvature (which is believed to cause secondary flow) of CT, often limits the maximum obtainable fluid injection rates. Therefore it is of practical importance to investigate the flow regularity and friction properties in CT. Professor Shah and his research team at the Well Construction Technology Center of the University of Oklahoma have conducted numerous theoretical and experimental studies regarding CT and have reported great achievements.

Chapter Four – Influence of Jetting Hole on Fracture Initiation and Propagation

Jetting hole geometry parameters definitely influence the fracture initiation and propagation in materials. This chapter introduces the numerical simulation and true triaxial fracturing experiments on hydra-jet fracture initiation and propagation. The Rock Fracturing Process Analysis software was used to calculate the fracture crack pressure and propagation. The investigated key parameters included perforation diameter, perforation depth, and the angle between perforation axis and the maximum horizontal stress. The results showed that the initiation pressure decreased as both perforation depth and diameter rose. The initiation pressure increased with increase in the angle. To quantify the complex fracture geometry, the fractal theory was employed and the fractal dimension was calculated.

Chapter Six – Operation Parameters Calculation

In this part, the related hydraulic parameters, including the nozzle numbers, pressure drop, flow rate, pressure loss along the tubing, and the prediction of the surface pump pressure, are presented in detail. The main contents show how to calculate the aforementioned parameters using corresponding equations and methods. According to the calculated results, the operators can determine the bottom-hole assembly, possible maximum pump pressure, and the total fracturing fluid volume, etc. At the end of this chapter, through a practical field case, the calculation procedure and results are listed in a table. Then the operators can clearly know the working steps and the materials consumed in every step.

Chapter Seven – Hydra-Jet Fracturing Bottom-Hole Assembly

As the critical components of this technology, the bottom-hole assembly, including its structure and the material, is very important to guarantee a successful hydra-jet multi-stage fracturing operation. This chapter presents the detailed structure and function of each part of the tool. First, the overall structure and the corresponding function are described in general. Then, the detailed structure of the jet sub and the slide sleeve inside is illustrated considering the possible risks in practical operations, like the pins strength, sleeves surface smoothness, and the jet sub or sleeve shoulder wear that results from proppant flowing, etc. Third, as the most important part of the technology, the nozzle inner structure and material are analyzed to get an effective jet for penetrating the casing and formation. A nozzle made of ceramics with a comparatively simple inner structure is adopted. Finally, the accessary parts, including the centralizer and one-way valve, guide, etc. are described briefly.