Ensuring Well Integrity in Deepwater using a fit for Purpose Advanced Cement System

Taoutaou, Salim; Azwar, Cinto; Pathak, Rakesh; Nana, Degaul; Ajwani, Prakash Anand

doi:10.2118/147550-ms

All Days 2011

DOI: 10.2118/147550-ms

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Ensuring Well Integrity in Deepwater using a fit for Purpose Advanced Cement System

Salim Taoutaou

Cinto Azwar

Rakesh Pathak

et al.

Abstract: Deepwater is one of the most technically and logistically challenging environments for cementing operations because of the risks associated with the conductor and surface casing cementing. Understanding the technical challenges, and mitigating the geological risks such as low temperature at seabed and fracture gradient, as well as shallow flow hazards including shallow water flow and gas Hydrates are key to designing cement slurries that can meet deepwater specifications and provide required zonal isolation. … Show more

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Cited by 4 publications

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Zonal Isolation through Gas Hydrates Offshore Tanzania

et al. 2013

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Deepwater cementing becomes increasingly challenging as drilling operations move to greater water depths and to more remote locations. Understanding these challenges and mitigating the associated risks in time has become very important tasks. Before the first exploration well for an operator offshore Tanzania was spudded in a water depth of 2580 m, an extensive analysis was performed to determine all the risks associated with cementing operations, especially in the increasingly challenging and critical surface casing section.The risks determined were low temperatures at seabed, unconsolidated formations close to seabed, potential shallow gas, and likely presence of hydrates. Because of the remoteness and limited oilfield infrastructure, logistics were also determined to be demanding. To successfully continue to drill further sections, the job objectives were zonal isolation across the shallow flow and hydrate zones, cementing back to seabed to provide a stable wellhead, and good cement around the casing shoe providing isolation for deeper formations.The cement job was designed to meet these challenges and objectives. Optimized particle-size distribution (PSD) cement slurry with low density was designed to avoid losses and still develop high compressive strength quickly at low temperatures. Low-temperature gas-migration additive and cement set enhancer were included to provide a short transition time preventing gas migration to seabed. Because of the lower cement ratio in the optimized PSD-blend, the slurry did not destabilize the hydrates during the setting process. The cement placement was simulated to confirm the job design would meet its objectives.Careful preparation and the optimized PSD-slurry system allowed executing the job meeting all objectives. Good zonal isolation and a successful leak off test were achieved, eliminating the contingency liner.

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Zonal Isolation through Gas Hydrates Offshore Tanzania

et al. 2013

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Overcoming Ultradeepwater Cementing Challenges in the Caribbean

Gupta

Bogaerts

Bellabarba

et al. 2014

Day 1 Wed, May 21, 2014

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Ever increasing energy needs have encouraged the operators to explore newer areas in deepwater. One of the high potential areas under exploration is the Caribbean basin, which includes Trinidad and Tobago, Suriname, Guyana and French Guiana. Due to the extreme environmental impact that can result from incidents occurring offshore, well integrity is a critical element in offshore development.. Cementing plays a major role in ensuring well integrity and this paper will cover various cementing challenges that were faced in Caribbean deepwater zones. The water depth of wells in Caribbean can be as much as 2300m with seabed temperature of about 4 ºC causing complex heat transfer and requiring fluid modeling software to accurately predict the bottom hole circulating temperature (BHCT) profile. Deepwater wells in the Caribbean can also be affected by the formation of gas hydrates. Cementing in hydrates requires cement slurries with low heat of hydration (HOH). The results from several field studies were used to select an optimum slurry design to successfully cement in hydrates. The wells in this area are also characterized by low fracture gradients with a narrow window between fracture and pore pressures. The cement jobs are designed with advanced computer aided design (CAD) to accurately simulate equivalent circulating density and assist in designing fluid placement within this narrow window. Engineered lost circulation material (LCM) can be used in fluids to achieve successful cement placement. Fluid modeling software also helps in optimizing mud removal by simulating the impact of centralizer distribution, optimizing spacer properties and more. To evaluate cement placement a combination of advanced acoustic logging-while-drilling (LWD) tools and pressure analysis can be used for deeper sections while for riserless sections, visual feedback from remote operating vehicle (ROV) can be used. A case study from Trinidad and Tobago and Southern Caribbean highlights some specific solutions and lessons learned.

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Overcoming Losses in Tophole Sections in Deepwater Namibia

Awalt

Bogaerts

Bonsu-Gyimah

et al. 2014

Day 1 Wed, September 10, 2014

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The continual increase in exploration drilling in southern Africa has translated into a number of remote deepwater campaigns, the most recent ones being in Namibia. One particular three-well campaign was exceptionally challenging as there was no near offset-well data available. The challenges were especially acute in the riserless tophole section.The well designs called for top of cement (TOC) at seabed for the surface casing. This was of the utmost importance for adequate structural and axial support for the blowout preventers (BOP) and subsequent casing strings. The very low fracture gradient near the seabed was the main challenge as the formations would not support the hydrostatic pressure of the cement column. On the first well, total losses were encountered prior to and during the entire cementing operation. As a result, no cement returns were observed at seabed, contrary to what was expected from hydraulic simulations and volume calculations and required to meet the job objective.To achieve objectives required for the success of the subsequent two wells, all aspects of drilling and cementing operations were reviewed based on the findings of the first well. Mud weight and casing setting depth were critically challenged, with other parameters adjusted. Cement formulation and density were optimized to reduce hydrostatic and hydrodynamic pressures and to increase the chance of success. The cement slurry was changed to a bimodal lightweight system with better fluid-and set-cement properties. Lost circulation fiber technology was also incorporated in the spacer preflush and in the cement slurry to mitigate any losses during placement.Alignment of service company and operator objectives and optimization of drilling and cementing parameters were critical for the successful cementation of these challenging tophole sections. Continuous improvements resulted in the second well being effectively cemented to seabed, even though intermittent losses were observed. After further optimization, the third well was cemented to seabed with full returns. Reaching the target TOC eliminated the need for a top-up job, saving valuable rig-time.

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Ensuring Well Integrity in Deepwater using a fit for Purpose Advanced Cement System

Cited by 4 publications

References 2 publications

Zonal Isolation through Gas Hydrates Offshore Tanzania

Zonal Isolation through Gas Hydrates Offshore Tanzania

Overcoming Ultradeepwater Cementing Challenges in the Caribbean

Overcoming Losses in Tophole Sections in Deepwater Namibia

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