A new cementing technology, top cement pulsation, can delay the static pressure loss of the slurry and effectively prevent gas migration under complex geologic conditions.1 2
When designing a cement job, cement quality is directly related to the chemical and physical properties of the slurry, thickening time, water loss, and formation permeability. Thus, under normal geologic conditions, simple additives such as retarders, accelerators, friction reducers, filtration-control additives, and lost-control material can generally be added to improve overall cement quality.
Under complex geologic conditions, however, severe oil and gas migration phenomena can occur while cementing, in some cases leading to well-control situations. Additionally, gas or water can create channels, or interzonal paths of communication can develop, which may or may not be detected with cement bond logs.
In 1995, Haberman developed a process to improve cement bond logs and to reduce or eliminate gas migration problems.1 The basic idea consists of injecting a pulse of relatively low pressure compressed air or water into the annulus at the surface after placement of the slurry. Basically, this injection process transmits a pressure pulse through the slurry at the speed of sound, resulting in a slower reciprocating motion in the compressible fluid phase (Fig. 1).2
In turn, the pulse pressure wave:
- Vibrates the slurry.
- Delays the thickening time of the slurry.
- Maintains the hydrostatic pressure over a certain time interval.
Subsequently, as the slurry thickens, hydrostatic pressure losses and conditions of uniform shear stresses are delayed, creating a deformed slurry column as it thickens. At the same time, the pulse pressure wave phenomenon prevents gas migration and improve cement bond logs.
With respect to delaying the hydrostatic pressure loss of the slurry, the main principle of this action can best be related to vibrational casing movements where up-and-down and rotational movements improve cement quality.4 5 None of these conventional approaches, however, have resulted in a practical means for well cementing under certain conditions.
Haberman's top cement pulsation (TCP) method, on the other hand, can be simply and inexpensively applied by relaying pulses of compressed air or water directly into the annulus, at the surface and above the slurry.2
To support Haberman's laboratory and oil field studies, mathematical models were developed by Southwest Petroleum and Xia'an Petroleum Institutes, China, to optimize TCP design (please see Equation box before following discussion).
Wave motion equation
According to practical condition cases, the Equation 16 boundary and initial conditions can be determined, so the solutions y=y(x, t) can be found. In this case, y is the displacement under the well depth x at time t. Additionally, y provides the displacement amplitude when y is maximum value at some time t.
Because the pressure pulses are transferred from top to bottom through the cement slurry, the y(L,t) displacement amplitude cannot be zero, and instead must be greater than some given value. Thus, the initial and boundary conditions can be determined to satisfy the given value.
The initial and boundary conditions are directly related to the parameters of compressor and pulse generator, so it provides the theoretical basis for the optimization of the parameters of compressor and pulse generator.
The factors and effects for wave motion in Equations 16 and 38 include the bulk modulus of slurry and wellbore rock, Poisson's ratio of rock, elasticity modulus of casing, slurry density and viscosity, plastic yield stress, annular inner and outer annular radii, gravitational acceleration, and so on.
Click here to view Propagation equations for top cement pulsation technique
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Pressure pulse waves
The solution for Equation 15 p(x,t) can be found after Equation 16 is placed under the initial and boundary conditions. In this case, the p(x,t) must be greater than the porous pressure of the formation in the study so that it can prevent gas migration into the slurry under complex geologic conditions. Otherwise, the initial and boundary conditions of TCP pressure wave will be designed again.
The authors thank the State Key Laboratory of Oil-Gas Reservoir Geology & Exploitation (Project No. PLN9908) of SWPI, P.R. of China, for its contributions to this article.
- Haberman, J.P., et al., "Method Apparatus to Improve the Displacement of Drilling Fluid by Cement Slurries During Primary and Remedial Cementing Operations and to Improve Cement Bond Logs and to Reduce or Eliminate Gas Migration Problems," U.S.Patent 5,377,753(1995).
- Haberman, J.P., "Reciprocating Cement Slurries After Placement by Applying Pressure Pulses in the Annulus," SPE/IADC paper 37619, 1997, pp. 383-92.
- Xisheng, L., "Drilling Technology Theory-Completion Engineering (in Chinese)," Oil Industry Publish, January 1994.
- Skalle, P., et al., "Vibration of Oil Well Cement," SPE paper 14508, 1992.
- Chow, T.W., et al., "The Rheological Properties of Cement Slurries: Effects of Vibration, Hydration Conditions and Additives," SPE Production Engineering, Vol. 3, September 1988, pp. 543-50.
- Morton M.D., Process Fluid Mechanics, Prentice-Hall Inc., Englewood Cliffs, New Jersey.
- Binder, R.C., Advance Fluid Mechanics, Prentice-Hall Inc., Englewood Cliffs, New, Jersey, 1958.
- Southwell, R.V., Theory of Elasticity, Oxford Clarendon Press, 1936.
Zhanghua Lian is a professor at the Center of Well Completion Techniques, Nanchong, China. He holds BS, MS, and PhD degrees in mechanical engineering from the Southwest Petroleum Institute (SWPI). Lian has also studied mechanical engineering and applied mechanics at the University of Michigan and petroleum engineering from Louisiana State University. He is now a professor, researching and teaching, in Center of Well Completion Techniques, PRC. Lian specializes in casing failure, rock and formation relationships, and perforated completions.
Jiang Hong holds a BS and MS from SWPI, specializing in transportation and storage engineering. He is an associate professor of research and teaching in the department of petroleum engineering at SWPI. Hong specializes in casing failure and stimulation technologies.
Wenkui Li holds a BS and MS from SWPI. He is currently an associate professor and works in Xi'an Petroleum Institute. His research interests include to rock mechanics, stimulation technology, well completion, rectification, and subsidy of production casing. Li has published three books, 38 papers, and holds nine national patents.