Wang Kelin

Review of Hole Cleaning in Complex Structural Wells

Complex structural wells are widely used in the development of marine oilfield, old oilfield and low permeable oilfield. However, poor hole cleaning is often occurred in the highly-deviated sections and horizontal sections of the complex structural wells, which affects rate of penetration and downhole safety. The methods to study cuttings transport can be normally divided into four types: 1) experimental observations, 2) CFD simulations, 3) theoretical correlations and models and 4) field tests. Experimental observations and CFD simulations are mainly used to analyze the effects of different parameters on hole cleaning and obtain some valuable data. Theoretical models and correlations are mainly applied to calculate cuttings bed height, critical velocity and etc to provide the guidance for the design of hydraulic parameters. The accuracy of the first three types are checked by field tests. In this paper, the effects of flow rate, inclination, mud rheology, drillpipe rotation and other factors on hole cleaning, and some typical correlations and models were briefly reviewed before 2000 years, and some new research findings were detailedly addressed. In addition, CFD simulations also were introduced. Although major improvements have been achieved in the past several decades, building a comprehensive and proven model requires much more experimental researches, CFD simulations, in-depth theoretic studies and field tests due to the complexity of cuttings transport under multi-factor interactions.

Review and Analysis of Cuttings Transport in Complex Structural Wells

Complex structural wells are widely used in the development of marine oilfields, old oilfield sand low permeable oilfields. However, poor hole cleaning often occurred in the highly-deviated sections and horizontal sections of the complex structural wells, which affects rate of penetration, cementing quality and downhole safety. It is advisable to study the behavior of cuttings transport under different conditions. In general, experimental observations and CFD simulations are main methods to analyze the effects of cutting parameters, fluid parameters and operational parameters on hole cleaning. The correlations and models are applied to predict the number of cuttings and the critical velocity in the annulus. In this paper, an analysis of key parameters is conducted on cuttings transport, the existing problems and characteristics of these correlations and models are summarized,, and different removal methods of annular cuttings and future research needs are discussed. Although major improvements have been achieved in the past several decades, how to accurately predict the cuttings bed height, critical velocity and other key parameters, and to effectively solve the poor hole cleaning still is a difficulty challenge. Therefore, more research will be conducted to further understand cuttings transport mechanism in multi-factors coupling and complex wellbore conditions.

Cuttings Transport Behavior and Simulation Analysis Affected by Hole Cleaning Tool

Researchers have designed many kinds of hole cleaning tools to improve hole cleaning condition in the com- plex structural wells. In this paper a mathematical model was built to analyzing the cutting particles movement on the helical blades of hole cleaning tool. The relationships between blade helical angles and cuttings transport velocity in tan- gential direction and axial direction are obtained by solving the model. The results show that blade helical angle as a con- trolling variable has a significant impact on application effect of the spiral hole cleaning tool; tangential cuttings velocity increases and axial cuttings velocity decreases with the increase in the helical angle and adjusting the helical angle can reach the required cuttings velocity.

Cuttings Transport with Gas in the Highly-Deviated Horizontal Wells

Gas drilling has been widely used due to its advantages of protecting and finding oil and gas reservoir, reducing lost circulation and pipe sticking, extending the bit life, and improving rate of penetration (ROP). Cuttings transport in highly-deviated and horizontal segment is considered as an important part of the design of hydraulic parameters. In this case, poor cuttings transport will lead to stuck pipe, higher drag and torque, slower ROP, bad cementing quality, and other problems. In this study, a two-layer steady model was developed to depict cuttings transport behavior, and the sensitivity analyses were conducted. The simulations show the ratio of bed area and annular area and pressure drop decrease with the increase of pipe eccentricity or inclination, and increase with the increasing gas density or gas viscosity. But the inclination, gas density and viscosity have a minor effect on cuttings transport.

Study on Cuttings Starting Velocity in Air Drilling Horizontal and Highly- Deviated Wells

Air injection rate as the key parameter of drilling air is directly related to the success of drilling procedure. In the previous studies, most of air injection rate models were built based on the vertical wells, which are not appropriate for horizontal and highly-deviated well and limit the wide application of air drilling to some extent. Based on the movement analysis of cuttings, this paper assumed that after the cuttings deposit to the low side of borehole, Air is injected to carry the cuttings out of the wellbore. Then, the starting velocity model in different hole angles is established through the stress analysis of cuttings motion, which can be used to calculate the minimum air injection rate. The numerical simulation results show that starting velocity of cuttings reaches the maximum in the hole angle 60-70 degrees. The larger diameter cuttings require a high starting velocity, which is difficulty to be transported. This means some appropriate methods should be applied for air drilling procedure, like using secondary crush tools. The subsidence degree is one important factor to the calculation model, and it is necessary to study cutting subsidence degree in next step.