After massive lost circulation resulted in plugging of one development well, an offset was successfully designed and drilled using Drilling with Casing technology, enabling drilling and casing of the bypass through the thief zone without losses.
The Eugene Island 364 field in the Gulf of Mexico is an area of rapidly deposited young and undercompacted sediments. As with any such area, fracture gradients, pore pressures and rock properties caused by undercompaction can play havoc with design assumptions. The younger, undercompacted clays take on the form of gumbo, slowing down drilling, inducing hole washouts, and causing "balling." In turn, bottomhole assembly balling can lead to swabbing and surging in the wellbore, especially in sensitive formations.
The subject well, A-2, had been drilled as part of a development in this field, offsetting well A-1. The A-1 well had experienced numerous geological, mechanical, and wellbore stability issues that ultimately resulted in failure to reach the objective and proposed total depth. To protect the productive zones drilled, the operator set casing across the shallow zones of interest and aborted the exploration tail.
The well design for offset well A-2 was developed based on lessons learned in A-1. Specifically, severe mud losses in the TB-4 sand were recorded in A-1, using oil-based mud (OBM). An overbalanced hydrostatic mud weight was determined to be the cause of the losses. The operator revised the predicted pore pressure model and imposed a real-time watch on pore pressure and drilling parameters while drilling the A-2 well. The operator also designed the intermediate hole to be drilled using water-based mud (WBM), with casing set below the TB-4 to isolate the thief zone encountered in A-1 and prevent lost circulation.
A 13.6-ppg WBM was used to drill A-2 through the TB-4, but the well still experienced severe mud losses. After evaluating various options, the operator chose to plug back the well and bypass the original hole rather than fight the severe losses and instability in the wellbore. A-2 was sidetracked with a maximum angle of 13.2° to the top of the TB-4 sand.
The well was then successfully drilled with casing for 269 ft through the TB-4, using a previously described drilling with casing system1 run with a liner which included a hydraulic set hanger and 3,438 ft of a 9 5/8-in., 53.5-lb/ft, HC P-110 casing with VAM SLIJ-II connections. The liner was run on 5-in. drillpipe. No mud losses occurred as the A-2 well was drilled with casing-an unexpected benefit in a section proven to be extremely sensitive to mud weight.
The initial objective for the offset well A-2 was to drill a delineation well and exploit the production potential found in A-1. The area is known for its young sediments and rapid deposition, characterized by unconsolidated sands, reactive shale or clay and gumbo to depths exceeding 10,000 ft. TVD. The pressure transition exhibits a multi-compartmental behavior beginning at 6,000 ft TVD, gradually increasing through numerous productive intervals to 7,000 ft.
