Industrial feasibility study for the use of barite as a permanent well barrier element

As more and more wells reach the end of their production life, the focus on permanent plug and abandonment has increased in interest. Cost-efficient abandonment of wells with ceased production is an important economic goal for the oil and gas industry. A dominant part of the plug and abandonment operation is the removal of steel tubular and casing to establish a rock-to-rock cross-sectional barrier in the well. This process is aggravated by settled barite and other mud solids accumulated at the bottom of the casing annulus, increasing over-pull and resulting in several cut and pull runs. If the settled barite, which is already in place behind the casing, could function as a part of a barrier envelope, it could significantly reduce such operations. This thesis’s primary objective is to investigate if industrial field data support the utilization of settled barite as a feasible annulus barrier element. A total of 307 wellbores were analysed for cut and pull operations, where attempts to circulate settled barite out of the annulus were performed. A three-layered model was suggested using theories of barite segregation and settling regimes in drilling mud. The model was used to calculate the hydrostatic pressure of an annulus column of drilling mud settlements to accurately predict the differential pressure excreted through the settled barite plug. Twenty-two of the investigated wellbores showed potential for further analysis, and four wells displayed plugs of settled barite that would prevent fluids from a re-pressurised reservoir to flow unintentionally to the surface or other formations

Industrial feasibility study for the use of barite as a permanent well barrier element

As more and more wells reach the end of their production life, the focus on permanent plug and abandonment has increased in interest. Cost-efficient abandonment of wells with ceased production is an important economic goal for the oil and gas industry. A dominant part of the plug and abandonment operation is the removal of steel tubular and casing to establish a rock-to-rock cross-sectional barrier in the well. This process is aggravated by settled barite and other mud solids accumulated at the bottom of the casing annulus, increasing over-pull and resulting in several cut and pull runs. If the settled barite, which is already in place behind the casing, could function as a part of a barrier envelope, it could significantly reduce such operations. This thesis’s primary objective is to investigate if industrial field data support the utilization of settled barite as a feasible annulus barrier element. A total of 307 wellbores were analysed for cut and pull operations, where attempts to circulate settled barite out of the annulus were performed. A three-layered model was suggested using theories of barite segregation and settling regimes in drilling mud. The model was used to calculate the hydrostatic pressure of an annulus column of drilling mud settlements to accurately predict the differential pressure excreted through the settled barite plug. Twenty-two of the investigated wellbores showed potential for further analysis, and four wells displayed plugs of settled barite that would prevent fluids from a re-pressurised reservoir to flow unintentionally to the surface or other formations