Effect of Gilsonite on drilling cement properties
Gilsonite is used in drilling cement as a lightweight mineral to reduce the weight of cement. However, by increasing the addition of Gilsonite, the weight decreases, but consuming more than 26% and mixing with cement and water cause separation of particles and flotation them on the surface of the slurry. Therefore, using other additives to suspend it in the slurry is essential. Bentonite is an industrial material to suspend Gilsonite powder in drilling. The combination of Bentonite, gillsonite and microsylica is extremely effective in creating a smooth scattering mixture.
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Control of loss circulation with Gilsonite Cement
Using Gilsonite in controlling and preventing loss circulation is not as efficient as Cotton Seed Shell, Mica and Walnut shell. For this reason, preventing and controlling loss circulation using just Gilsonite, is not recommended. The effect of Gilsonite in reducing drilling cement weight is more than its role in lost circulation prevention.
Due to the specific weight and the amount of water needed, not only the cement weight become lighter, but also the amount of required water also decreases.
The normal consumption of Gilsonite is 6 to 26 percent by weight of cement. In higher amounts, mixing and laying the slurry faces problems. In addition, as the concentration of Gilsonite in the slurry increases, the weight loss rate of the slurry decreases and only at lower concentration values, the highest weight loss is achievable. After this stage, the reduction amount is quite low compared to the initial values.
Other Gilsonite features for drilling Cement
For production of Gilsonite slurry used in cementing, the different amount Bentonite is required to increase the viscosity of slurry. If the slurry does not have enough viscosity, Gilsonite’s light beans come to the surface and slurry uniformity is destroyed. It is certain that within 24 hours at a pressure below the 68/68 MPa (PSI 3000), the compressive strength of MPa 44/3 (PSI) is achievable.
The results of the well cement operations have shown that Gilsonite cements are more capable for filling fragile and broken zones than any other cements. Gilsonite cement due to having two properties (controlling loss circulation and reducing weight) can circulate in wells that have loss circulation even with lighter slurry. In this condition, without any cement lost circulation, seams and gaps are blocked.
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Cementing oil and gas wells
Cementing oil and gas wells is done by various methods to complete the well, preparing the well for drilling, testing and installing equipment. In deeper drilling, to keep the strength of the well, cementing is more important. In order to meet this need, various methods, equipments and chemicals are used. Over time, these methods have changed and gradually improved. But experiments to improve the properties of drilling cement are still ongoing.
Initially, several types of cement and cement additives became common in the oil industry. In the following years, in addition to the construction of factories manufacturing cementing equipment, units were established for researching the impact of chemicals on improving the properties of cement. The most important tasks of these units were performing tests on various types of cement, designing and evaluating the slurry after usage inside the well, and conducting well pilot tests to obtain better results at the wellhead.
Today, due to the high cost of oil and gas wells, increasing the depth of wells, temperature and pressure conditions at great depths, it is necessary to use various additives and cements depending on the depth and temperature of the well. Also, according to the weight of the wall pipes in proportion to the thickness to withstand different pressures, methods should be designed to reduce the weight of the pipe and the cement that hangs from the surface or end of the previous wall pipes. In recent methods, in addition to using software to design drilling cement suitable for well conditions in laboratories, attempts are made to make various slurries in temperature and pressure conditions and other effective factors inside the well.