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Biswal, Debakanta (Adani Welspun Exploration Limited) | Nedeer, Nasimudeen (Adani Welspun Exploration Limited) | Banerjee, Subrata (Adani Welspun Exploration Limited) | Singh, Kumar Hemant (Indian Institute of Technology)
The boundary between a thick carbonate layer and its substrata is often a well-defined reflector due to the presence of shaly and clayey layers beneath the carbonates. This reflector and other underlying reflectors result in a velocity pull-up effect because the seismic velocities within the carbonates are higher than that of the surrounding sediments. The geometry of velocity pull-up beneath the carbonate body is related to the geometry of the structure and the thickness of the carbonate body the seismic wave travels through.
In B9 area of Mumbai Offshore basin, the reservoir facies are largely represented by clastics deposited along tidal deltaic lobes. Wells drilled though Daman formation have encountered good quality pay sands within the Daman formation. This pay has produced commercial quantities of hydrocarbons in the vicinity making the area attractive for further exploration and exploitation. The overlying Bombay formation consists mainly of shale with occasional bands of limestone and claystone. The development of thick isolated carbonates bodies within Bombay formation is observed in "C" structure on which "Well-C" is placed. This is seen to significantly constrain the structural configuration in the "C" area. There is a possibility of substantial extension of the "C" structure towards south if the impact of velocity pull up due to carbonate build up can be successfully mitigated. The ultimate challenge is to image the Daman reservoirs, mitigating overburden lateral velocity variations.
In addition to a layered cake depth conversion approach for depth conversion of the time map, a more robust approach, PSDM followed by depth conversion was carried out. This paper highlights the merit of different methods.
A well in the Panna-Mukta-Tapti Joint Venture (PMT JV) was completed using an isolation valve as the method of isolating the reservoir whilst running the completion into the well. Mechanical failure to open the valve was not anticipated as the isolation valve had a successful history in the JV with no failures in the last 10 years. However, in this well, the isolation valve failed to open. After spending multiple days attempting to open the valve and diagnosing the cause of the failure, it was concluded that the isolation valve was mechanically stuck.
Further evaluatios of solutions incorporating Coil tubing (CT) and e-line interventions concluded that standard milling operations would pose additional challenges for the well due to the design of the completion below the isolation valve. Subsequently, a unique, star shaped milling bit was designed and manufactured to enable milling of the isolation which was smaller than 2.56" SSD and landing nipple present below the isolation valve. This was required to ensure future access for interventions through the SSD and landing nipples is not compromised and milling out the coupon from the flapper isolation valve does not get stuck in the smaller ID completion profile below it.
The newly designed bit enabled milling and subsequently expanding that hole to the desired OD of 2.7" which would allow for future interventions. E-line milling was selected due to limitations in control with CT for debris generated. The total time from identification of the problem to designing, manufacturing, testing the new bit, transporting it to India and executing the solution was 45 days. The operation itself was carried out within 45 hours vs 120 hours projected with CT, leading to a significant cost saving, equivalent of 3 times daily spread rate for the rig. This unique methodology also enabled early onset of production, avoiding a delay of approxmately three month.
This was the first time this new mill bit was applied and the first time that this isolation valve had been milled out using E-line. Existing, standard bit designs were not sufficient to accomplish this solution nor were conventional approaches satisfactory in today's economic climate. This paper will present the significant benefits accomplished from the utilization of the robotic, electric-line (e-line) intervention to mill out a malfunctioning isolation valve versus the use of coiled tubing (CT).
In addition, it will use the flexibility and control features of e-line based, intervention technology towards addressing short lead time and design modification required to meet dynamic well challenges.
This paper presents the significant benefits accomplished from the utilization of robotic, electric-line (e-line) intervention to mill out a malfunctioning flapper valve versus the use of coiled tubing (CT). In addition, it will discuss the flexibility and control features of e-line based, intervention technology towards addressing short lead time and design modifications required to meet dynamic well challenges.
On the West Coast of India a well was completed using a flapper valve as the method of isolating the completion while being installing it into the well. A standard practice in the field, the flapper valve has been utilized successfully for a decade without any failures. Hence, during the current operation, contingencies to overcome a mechanical failure to open the valve were not on board. And unfortunately, in this particular well, the flapper valve failed to open as per SOP.
After multiple days spent on attempting to cycle open, attempts were then made with slickline to determine if debris accumulation was an issue. When this proved false, it was concluded that the flapper valve was mechanically stuck.
After evaluation of solutions incorporating CT and e-line interventions, it was determined that standard milling operations would pose additional challenges for the well due to the design of the completion below the flapper valve which incorporated a 2.56" restriction. If the milled portion of the flapper valve was not retrieved there was consequential risk that the well could become plugged by the coupon.
After an extensive review with the PMT JV (Panna, Mukta and Tapti Joint Venture) plus the Design and Engineering team of a service provider, it was agreed that the probability of retrieving the milled fIapper valve coupon with standard bits was low. However, the service provider suggested a unique, star shaped milling bit that enabled milling a coupon which was small enough to pass through the restriction should it not be captured. E-line milling was selected due to several reasons including the finer control, efficiency of operations and minimum debris generation.
The newly designed ‘star’ bit enabled milling a small coupon and subsequently expanding that hole to the desired OD of 2.7" which would enable access for future interventions as needed. The total time from the identification of the problem to designing, manufacturing, testing the new bit, transporting it to India and executing the solution was less than 45 days. This enabled the well to be intervened upon while the rig was on the platform. The operation itself was carried out within 45 hours vs the 120 hours projected for CT, leading to a cost saving of ~ 750,000 USD. This unique methodology also enabled early onset of production, avoiding a delay of ~ three months.
This was the first time this new mill bit was applied and the first time that this type of flapper valve had been milled out. Existing, standard bit designs were not sufficient to accomplish this solution nor were conventional approaches satisfactory in today's economic climate.