Safe Drilling Technology for Horizontal Wells in Ultra-Thick Salt-Gypsum Rock in The Right Bank of The Turkmen Amu Darya

Abstract

Abstract The formation of Section B, which is on the right bank of the Amu Darya consist of high pressure salt and gypsum formation. The average thickness of the salt-gypsum layer is about 900 meters, the maximum pressure coefficient is 2.3 g/cm3, the salt rock is easy to creep, resolve, and crystallize. The salt layer is close to the reservoir. Wellbore path is difficult to control. The drilling accident rate is 34%, and the success rate of high pressure brine drilling is 0, which leads to the fact that no horizontal well drilling has been carried out. In order to develop the safety technology, it is necessary to carry out the large angle orientation drilling method in the high-pressure salt water and salt-gypsum layer. However, this kind of method has not been widely used, so it is urgent to solve the safe drilling problem and orientation problem of the high pressure salt paste layer. The proper proportion of drilling mud in the salt-gypsum layer is optimized by establishing the bore shrinkage equation and using the layer control method to determine the pressure of the salt-gypsum layer. After that, the unsaturated saturated brine drilling fluid system compatible with the salt rock layer is selected. After the salt-gypsum layer is sealed with casing tube, the reservoir will be re-drilled. The slope will be designed in the salt layer, and the tricone bit control will be carried out by adding the cone bit and selecting the MWD directional drilling tool combination. The proper density of the well drilling mud will prevent the salt rock from creeping and high pressure salt water from flooding. The stable saturated brine drilling mud will then be controlled effectively, and the stability of the well bore caused by salt losing is effectively controlled. The well bore expansion rate dropped from 19% to 2%; with salt-gypsum layer is sealed with 250.8mm thick anti-extrusion casing, and the water expansion packer is installed, which effectively prevent high pressure salt water channeling and casing tubes collapsing. After that, it is easy to control the drill direction angel in the high-pressure salt gypsum formation between 0° and 80°. After putting the directional drilling tool in the centralizer position and combined with other skills, the drilling speed has been increased by 8.7%. Up till now, the horizontal drilling technology has been widely used in the zone. 50 wells have been using this drilling technology and goes on well.