RIASSUNTO
SPE Members
Abstract
A high pressure salt water influx was encountered while drilling a Deep Exploration well at 20,363 ft. Attempts were carried out to control this influx but the well killed itself. The fishing operations revealed the drill pipe to be plugged with salt balls. The paper describes and analyses the phenomenon paper describes and analyses the phenomenon that resulted in the formation of the salt balls which subsequently plugged the drill pipe and led to the killing of the well. pipe and led to the killing of the well. 2.
Introduction
The onshore exploration for gas in the Khuff formation of the Emirate of Abu Dhabi started in 1980. The first Khuff well was drilled in Bu Hasa field to a depth of 20,363 ft where a highly pressurized salt water influx was encountered. The bottom hole pressure build-up extrapolation indicated 21,080 psi at this depth with a bottom hole static temperature of 440F.
A constant influx of salt water contaminated the mud during the killing operation and large quantities of salt were evident on the Shale Shaker screens.
During the initial killing operations drill pipe parted at 11,860 ft. The killing pipe parted at 11,860 ft. The killing operations were continued by bullheading mud and fracturing the formation. An underground water flow from the drill pipe fish and down annulus into a thief zone was suspected. The well subsequently died and the top section of drill pipe was recovered. Fishing operations then proceeded and three sections of drill pipe were cut and recovered to a depth of pipe were cut and recovered to a depth of 12,882 ft. The fish was found to be plugged with balls of 99.9% Sodium Chloride identical in size and colour below 12,633 ft.
The Investigations and analysis which have been carried out to determine the structure of the salt balls indicated that their crystallization may have been generated by cooling or thermal gradient effect enducing an over-saturation of the solution.
3. DESCRIPTION
3.1 WELL DESIGN:
The formation of the salt balls occurred in the first deep Khuff well drilled onshore Abu Dhabi Emirate in the Bu Hasa field (Fig. 1).
The first Khuff well was designed according to the information collected from the other Khuff wells drilled in the area. The well was designed with 10,000 psi pressure rating for casing scheme and psi pressure rating for casing scheme and wellhead configuration (Fig. 2).
3.2 STATUS and CONDITIONS OF THE WELL PRIOR TO THE KICK:
The well was spudded in October, 1980. The 30"", 20"" and 13.3/8"" casings were set without major problems.
The 12.1/4"" hole was drilled to a depth of 16,053 ft when a kick was experienced from the Jilh formation. Estimated formation pressure gradient was 0.72 psi/ft. psi/ft. A heavy 9 5/8"" liner was successfully run and cemented with shoe at 15,800 ft (i.e. above the kick depth).
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