Zhongwei Huang

Abrasive Water Jet Perforation—An Alternative Approach to Enhance Oil Production

Abstract This article investigates the mechanisms, the results of laboratory experiments, and the results of field tests on the abrasive water jet (AWJ) perforation for enhancing oil production. The mechanism investigation showed that the AWJ perforation is a two-stage process, the ductile casing erosion stage and the brittle rock penetration stage, and each stage follows different failure mechanisms. The laboratory AWJ-parameter experiments were conducted on pressure, flow rate, abrasive material, abrasive granule size, abrasive flow rate, ambient pressure, rock material, and exposure time. The field tests of 10 oil wells (11 runs) illustrated that the AWJ perforation depth could reach about 0.78 m with pump pressure of 45–60 MPa at different formations, while the location error was less than 0.1 m. The oil production rate comparison, before and after implement, showed the AWJ perforation technology can effectively and prominently enhance oil production.

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.

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.

STUDY OF TREATMENT OF NEAR WELL-BORE FORMATION PROCESSED WITH HIGH PRESSURE ROTATING WATER JETS

ABSTRACT High pressure water jet removing impurities in formations is a new way developed recently to increase oil production and injected-water. First of all, this paper presents the main reasons of formation plugging, the basic principles of high pressure rotating water jets removing impurities and the laws of the tools rotating speeds, impact pressure and relations between impact pressure and nozzle stand-off. The field-test results obtained from over 500 oil and water-injection wells in Liaohe, Shengli, Zhongyuan, Huabei etc., indicate that this technology has such advantages as simplicity of use, cost effective, high success rate, wide adaptability, and significant effectiveness. From this, it is profitable and promising to increase production in highly water-cut oilfields.

Investigation And Application Of Multistage Hydrajet-fracturing In Oil And Gas Well Stimulation In China

Multistage hydrajet-fracturing combines abrasive jet perforating and hydraulic fracturing to perform separate, sequential fracture stimulations without mechanical packers. It can reasonably place fractures according to geological condition, and then accurately treat them. Without packer, it uses dynamic isolation to seal flow into target, saving operating time and lowering operating risk. Therefore, the process not only adapts to stimulate open hole, but effectively treats liner or cased completions. The mechanisms and fluid dynamics of multistage hydrajet-fracturing technology are investigated with numerical simulation and laboratory experiments. More than 30 oil and gas wells have been successfully treated using this technology since 2007. On average, three hydraulic fractures with total 120m proppants were placed at strategically selected locations in well, typically several hundred meters apart without sealing equipments. The deepest treatment in oil well 203-19 in Zhongyuan oilfield, using tubing string, was 3692m, and surface pressure reached 88MPa. Significant stimulation results were achieved in these wells. For example, production increased by more than 50 times after stimulation to the gas well XS311H in Sichuan oilfield. The oil well 92-2 in the Zhongyuan oilfield, which had been a dead horizontal well, has been revived using this technology with average oil production of 15 tons per day. Multistage hydrajet-fracturing stimulation shows promising feature for horizontal, vertical, deviated, and even multilateral wells. Introduction Recently, more and more attention has been paid to the development of low permeability reservoirs in China. Stimulation treatment has been the main method exploiting these reservoirs. In some oilfields, almost every well needs fracturing or acid treating. In recent years, multistage fracturing in horizontal wells and vertical wells becomes a preferred stimulation method to increase oil production (Li Gensheng et al. 2009). Common methods of stage fracturing include temporary plugging fracturing, limited entry fracturing, mechanical packer assemblies, and so on. Temporary plugging fracturing is appropriate for open-hole stimulation. However, this method is difficult to control the location of crack initiation along wellbore. Limited entry fracturing is suitable for many new wells completion, especially wells with thin beds. It is necessary to optimize the perforating scheme and calculate cave friction accurately. Mechanical packer assemblies are mainly applied in cemented-cased wells, and seldom used in bare-hole or slotted liner wellbores. In addition, some packers are likly to be sticked during stripping operation, increasing potential risk. Hydrajet-fracturing technique (HJF), as an alternative stimulation method, does not require mechanicial packers and can achieve several stages fracturing treatment in only one service trip. Now HJF has proven to be an economical, effective, and low risk multistage fracturing process. The HJF method was put forward in 1998 by Jim B. Surjaatmajda et al., Hallibuton engineers (J. B. Surjaatmadja 1998). They did many laboratory experiments and oilfield tests in Texas and New Mexico of United Stated successfully (Jim B. Surjaatmadja, et al. 2002). In the past decade, HJF application has expanded around the world. There are many successful cases in complex structural wells, either hydraulic fracturing or acid fracturing treatment. A number of cases applied coiled tubing delivering the BHA safely and quickly (Mc Daniel, B.W. et al, 2004). Remarkably, in 2003 its first offshore

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.

Surface Experiment of Abrasive Water Jet Perforation

Abstract This article presents the experiment process and results of abrasive water jet perforation. This experiment was conducted in Kalamayi, China, Xinjiang Oilfield in October 2004. Referring to explosive perforation experiment, we made two cement cylinder samples with a diameter of 2.4 m, 1.2 m high, putting a 139.7 mm (5-1/2″) and a 177.8 mm (7″) casing sub in them, respectively. The two cylinders were buried underground. During the experiment, we changed the following parameters: blasting time, nozzle diameter, and cement cylinder property. After experiment, we opened the cylinder and found that, compared with explosive perforation, the hole on the casing wall and the tunnel in the cement were much rounder and bigger than with that method. In addition, it can cause a fracturing effect, possibly forming micro-fractures on the tunnel wall. This effect can avoid forming impermeable crushed zone when using explosive perforating.