An Innovative Solution for Preventing Gas Migration through Cement Slurry in the Lower Indus Basin of Pakistan

Abstract

The integrity of well construction plays an important role to recover the hydrocarbons from subsurface to surface safely and economically. The poor cement integrity behind the casing becomes the cause of gas migration and ultimate well abandonment. The lower Indus basin of Pakistan has the majority of gas producing wells and some of them are plugged due to poor cementing. This is caused by the substantial decrease in the performance of cement slurry with increase in temperature as a function of depth. Therefore, it is essential to improve the API properties of cement slurry at high temperature for minimizing fluid loss and preventing the gas migration. For this purpose, different types of polymer have widely been used as the additives in cement slurry, but those polymers show thermal thinning behavior above 158 °F temperature. Polymers have also been modified by adding chemicals to improve their thermal stability range. However, the addition of chemicals affects the properties of other additives and increases the cost of cementing operation. This paper presents the incorporation of Hydroxypropylmethylcellulose (HPMC) cellulose type polymer in cement slurry which acts as a thickener, film foamer and water retention agent. It is capable of increasing the viscosity at elevated temperature. The viscosity of HPMC solutions was determined experimentally at different temperatures ranging from 86 °F to 212 °F with respect to shear rates. The HPMC polymer showed remarkable rheological properties as a thermal thickener at 194 °F. HPMC solution was then combined with cement slurry to evaluate its API properties such as rheology, fluid loss, free water settling, thickening time and transition time at 194 °F. The experimental results showed that HPMC based cement slurries have significant rheology, minimal fluid loss, zero free water, extended thickening time. The transition time of slurries was less than 45 minutes which is considered as the excellent cement slurry for preventing gas migration as per API standards. It is concluded that HPMC based cement slurries performed as the multifunctional additive, which successfully improved the properties of slurry and prevented the gas migration at high temperature. Hence, field application of HPMC polymer will be a prominent and a cost effective technique for the petroleum industry during cementing operation in the lower Indus basin, Pakistan.

Enhancing Characteristics of Well Cement Slurry Using Cellulose Based Polymers

“…Cement used in producing wells for repairing purpose or remedial work. To unsuitable selection of additive and substandard designing of cement slurry generates problems like that loss of fluid and separation of free water, which becomes derivation of well evacuation (Irawan et al, 2018).…”

Possibilities of Limiting Migration of Natural Gas in Boreholes in the Context of Laboratory Studies

“…Limitation of uncontrolled natural gas flows from the ring and/or annular space of a borehole is one of the crucial aspects during sealing of casing in boreholes drilled in formation with a higher risk of gas migration (the so-called exhalation). It relates to the main objective of casing sealing, i.e., ensuring durability and tightness between the lowered casing, on the one hand, and the drillhole wall and the previously cemented casing string, on the other [1][2][3][4][5]. As there are cases of gas invasion into the structure of the bonding slurry, resulting in leaks in the structure of the cement coating, it is necessary to carry out research and development work aimed at continually improving the quality of cement slurries formulations and the slurry injection technology [2,[5][6][7].…”

“…It relates to the main objective of casing sealing, i.e., ensuring durability and tightness between the lowered casing, on the one hand, and the drillhole wall and the previously cemented casing string, on the other [1][2][3][4][5]. As there are cases of gas invasion into the structure of the bonding slurry, resulting in leaks in the structure of the cement coating, it is necessary to carry out research and development work aimed at continually improving the quality of cement slurries formulations and the slurry injection technology [2,[5][6][7]. During cement slurry bonding, in the process of its hydration, gel structure is created and at that time a clear decline of hydrostatic pressure in the ring space of a drillhole is observed.…”

“…During cement slurry bonding, in the process of its hydration, gel structure is created and at that time a clear decline of hydrostatic pressure in the ring space of a drillhole is observed. When slurry changes its structure, it is very likely that gas moves in the gelled slurry structure, which may consequently result in gas migration both through fresh and hardened cement slurry [2,3,5,[8][9][10][11][12][13].…”

“…When developing sealing slurry formulations, various additives and admixtures are used in order to reduce the possibility of uncontrolled gas flows in boreholes through the setting slurry and after it has set, i.e., microcements, microsilicas, nanosilicas, which tighten the microstructure, as well as latex and cationic polymers, which shorten the gelling time of the slurry and thus reduce the possibility of natural gas flowing through the hardened cement slurry [2,13,[21][22][23][24]. When developing sealing slurry formulations, various additives and admixtures are used in order to reduce the possibility of uncontrolled gas flows in boreholes through the setting slurry and after it has set, i.e., microcements, microsilicas, nanosilicas, which tighten the microstructure, as well as latex and cationic polymers, which shorten the gelling time of the slurry and thus reduce the possibility of natural gas flowing through the hardened cement slurry [2,13,[21][22][23][24]. When developing sealing slurry formulations, various additives and admixtures are used in order to reduce the possibility of uncontrolled gas flows in boreholes through the setting slurry and after it has set, i.e., microcements, microsilicas, nanosilicas, which tighten the microstructure, as well as latex and cationic polymers, which shorten the gelling time of the slurry and thus reduce the possibility of natural gas flowing through the hardened cement slurry [2,13,[21][22][23][24].…”