No abstract

Durability and long-term integrity of oil well cement are the most important parameters to be considered while designing the cement slurry, especially in the high-pressure and high-temperature (HPHT) environments. In this study, the effect of adding the polypropylene fiber (PPF) to Saudi Class G cement is evaluated under HPHT conditions. The effect of the PPF on the cement compressive and tensile strength, thickening time, density, free water, porosity, and permeability was studied. The effect of the PPF particles on the cement sheath microstructure was studied through powder X-ray diffraction (XRD) and scanning electron microscope. The results obtained showed that PPF did not affect the cement rheology, density, and free water. The addition of PPF considerably decreased the thickening time and improved the tensile and compressive strength of the cement. 0.75% by weight of cement (BWOC) of PPF reduced the thickening time by 75%, from 317 to 78 min. The compressive strength of the cement increased by 17.8% after adding 0.5% BWOC of PPF, while the tensile strength increased by 18% when 0.75% of PPF is used which is attributed to the formation of stable forms of calcium silicate hydrates because of the ability of PPF to accelerate cement hydration process as indicated by the XRD results. The ability of the PPF to decrease the cement thickening time along with its ability to improve the cement strength suggests the use of PPF as an alternative for silica floor in shallow wells where a reduction in thickening time will decrease the wait on cement time. Porosity and permeability of the base cement were also decreased by incorporating PPF because of the pores filling effect of PPF particles as indicated by the microstructure analysis.

With the high global demand of oil and gas, oilfield companies are seeking resources in the unexplored areas by drilling wells to explore the potential reserves of oil and gas. The drilling process has become more challenging in these unexplored areas, especially at the high pressure and high temperature conditions (HPHT). A strong cement sheath is highly desired to ensure the durability and integrity of the wells to overcome these challenges. The cement slurry design and cementing job become more challenging especially when the process is carried out at the high pressure and high temperature conditions. Industry is always looking for the new material which can be stable at these extreme conditions and meet the requirement effectively and economically. Polymer fibers are being used in the petroleum industry lately to assist in meeting these tough requirements. In this research, the usage of polypropylene fibers (PPF) on enhancing the oilwell cements properties at high pressure and high temperature (HPHT) were evaluated. The polypropylene fibers were added into cement admixture with discrete amount to evaluate its influence on enhancing the performance of cements especially those relate to the toughness. Experiments were performed using distinct cement slurry characteristics such as rheological properties, thickening time, compressive strength, density, porosity and permeability. The Scanning Electron Microscope (SEM), and X-ray powder diffraction (XRD) was also performed for analyzing the microstructure of the cement. The experimental tests showed that addition of fibers improves the mechanical properties, accelerates the thickening time, reduces the porosity and permeability and helps in designing a new cement slurry which withstands the HPHT conditions. Polypropylene fiber has a significant effect on reducing the porosity and the permeability of the base cement. Microstructural analysis showed that polypropylene fiber particles block the capillaries by filling the pores in the cement, so a dense cement structure is achieved.

In deeper wells, high pressure and temperature post cementing operations put extreme stresses on the cement sheath and dramatically affect the cement integrity. So, the design of the cement slurry is very important to ensure the durability and long-term integrity of the cement sheath. The design should lead to a better zonal isolation and strengthen the bonding with the casing. Furthermore, it should help to shield the casing from corroding and unpredictable shock loads in deeper zones and sustain plugs to control the lost circulation in fractured and high permeability zones. Different additives were used to provide these functions such as; polymers, fibers, and bio-medicine in concrete history. Because of their large surface areas and small size, those particles are highly being used in the petroleum industry in the latest decades. In this study, the usage of polypropylene fibers (PPF) is evaluated for oil well cement at high pressure and high temperature (HPHT) condition. The polypropylene fibers were added to the base cement in a different amount to evaluate its influence on enhancing the performance of cement. The results obtained showed that adding polypropylene fiber to the base cement has a negligible effect on cement density, rheological properties, and free water. Using polypropylene fiber (0.75% base weight of cement (BWOC)) with the base cement reduced the thickening time by 75%; from 317 minutes to 78 minutes. The addition of Polypropylene fiber (0.5% BWOC) increased the compressive strength of class G cement by 17.8%. Polypropylene fiber can be used as an alternative material for silica floor in shallow wells. Polypropylene fiber has a significant effect on reducing the porosity and the permeability of the base cement.