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Gas leakage through cement in the annular space around a cemented casing is still a serious problem although new additives and improved techniques have reduced the problem. A new approach is the construction problem. A new approach is the construction of an emulsion cement, consisting of a double emulsion; water-in-oil-in-cement. Waterdroplets containing a controlled number of species are emulsified into mineral oil. This W/O emulsion is then emulsified into the cement slurry in small amounts (3-15 vol %). The effect of the emulsion on the cement slurry has been recorded through standard API tests. In addition the bond between cement and steel surfaces and the tightness against gas migration have been checked. Compared to other cement slurries, the emulsion cement shows promising results with respect to becoming a friction reducer and an anti gas migration additive. Further tests are necessary to determine the applicability of emulsion cement. Cement slurries behave different at high temperatures, and test procedures and test equipment must be improved in order to comply with down hole conditions.
STATEMENT OF THE PROBLEM
In sedimentary formations containing gas, known cementing techniques will frequently create problems like gas entering the annular space after the cement slurry has been pumped in place. Gas can flow through minor channels or pores in the cementing slurry from a high pressure zone into a lower pressure zone. Sometimes the gas can penetrate to the surface, or it can be penetrate to the surface, or it can be stopped at the well head. This type of gas migration can be dangerous and give blowouts and accidents. Even if the leakage is discovered before this happens, expensive repairs may become necessary.
The causes of gas migration are caused by
- free water - loss - poor bonding to the surroundings - loss of hydrostatic pressure
Free water that is emitted during the hardening and settling process can develop water pockets in the hardened body. These water pockets can evolve into communication channels for gas when the water is suppressed.
Chemical processes, temperature variations, and filtrate loss can cause creeping of the cementing slurry during the solidifying and hardening period. Mechanical stress during the following drilling and perforating operations may create cracks in the cement.
Difficulties in obtaining good contact between the cementing slurry and the environment, and in suppressing the drilling mud may cause channels and gas migration. Before the solidifying process starts, the cement behaves like a liquid transferring hydrostatic pressure depending on density and depth. Early in the process, the cement stops behaving like a liquid, but rather as a plastic slurry with weak bonds and with free water in the voids. A volume reduction of the free water in the void structure will then cause a pressure reduction. Even with additional substances in the cementing slurry, which reduces the filtrate, water loss cannot be totally prevented.
Abstract A water-disperible particulate system has been widely used in many mature oilfields for reservoir conformance control. This paper discusses performances of a newly formulated grafted bentonite to reduce the permeability and build up flow resistance in highly permeable water channeling zones. In this study, effects of various salinities, different injection flow rates and shear rates were investigated in the laboratory to determine permeability reduction ratio and transport properties to improve reservoir conformance problems. A flow model was set-up using sandpack flooding system where the sandpacks were saturated with brine. Experimental results obtained revealed that the grafted bentonite is easily injected and gradually built flow resistance by particles straining, physical-chemical attachment, and swelling. The permeability reduction ratio increased with increasing salinity while it decreased with increasing velocities. A significant permeability reduction ratio was observed when 0.5 pore volume of grafted bentonite dispersed in 1% NaCl brine was injected into brine saturated sandpack column. These significant results highlighted new insights for successful applications of modified bentonite to improve reservoir conformance problems.
The principles of the adsorption of polyacrylamide (PAM) and partial hydrolyzing polyacrylamide (HPAM) on clay particles and the factors affecting the adsorption are studied theoretically and experimentally. Several isothermal adsorption models are analyzed and compared with the experimental data. It is concluded that the adsorption of PAM on clay particles needs about 2 hours to reach a dynamic equilibrium, and the model developed by Simha-Frish-Eirich is the best model to describe the adsorption processes.
PAM and HPAM have been extensively used in drilling fluids, polymerflooding, water plugging and water treatment, etc. The results of these applications are closely related to the adsorption principles on clay particles. This paper is mainly focused on the application of drilling fluids.
Abstract Drilling fluid is a vital element of the drilling process. Any drilling fluid must have common properties that facilitate safe and satisfactory completion of the well. The main component of water base mud is clay (mostly bentonite). The present consumption of bentonite clay in the drilling operations in Saudi Arabia alone can reach over 100 thousands tons a year and all of it is imported from USA. This trend is expected to continue as drilling activity increases. The large consumption and the high importation cost of this material lead to an attempt to find a local substitute. Clays in Saudi Arabia are represented by numerous commercial stocks. The use of these local clays in the drilling activities can save a huge amount of hard currency that otherwise would be spent on importing it from abroad. Several attempts were made to investigate shale outcrop precipitates in the kingdom. This work focuses on the possibility of the utilization of local bentonite clay minerals as a basic material for drilling fluids used to drill oil and gas wells. The only known bentonite outcrop in the kingdom is in Khulays area, 70 km north Jeddah adjacent to Makkah-Madinah road. API specifications for acceptable drilling mud was the base for evaluating the local bentonite The properties of the local mud can be improved economically by adding some cheep materials to the prepared mud to enhance its viscosity and filtration loss (such as CMC, Drispac polymer, and bentonite extenders). Also shearing speed can be used as an enhancement method to improve the dispersion rate of the clay suspension, and hence increase viscosity and decrease filtration loss. But the used shearing speed should be limited to a practical and economical speed. The bentonite extender can be either a salt or a polymer, it enhances viscosity buildup by slightly flocculating the bentonite suspension. Sodium carbonate is an example of a salt that can be added as an extender. Soaking raw bentonite with a solution of sodium salt resulted, through ion exchange, in a higher sodium bentonite content. More effective extenders than inorganic salts are the high molecular weight linear polymers.