Design Transformation of Hydraulically Powered Coiled Tubing Tractors for Matrix Acidizing Stimulations in Extended Reach Carbonate Reservoirs

Abstract

Abstract The deployment of hydraulically powered coiled tubing (CT) tractors for matrix acidizing stimulations in extended reach carbonate reservoirs have provided critical benefits to well productivity. The technology allows for uniform placement of the matrix acid treatment while ensuring good zonal coverage. There have been several innovative tractor technologies developed over the last few years and the latest advances in design required an ‘out of the box' solution. For oil producers with electrical submersible pumps (ESP) completions including bypass sections, the 2.4" restriction in tubing size requires a large expansion ratio once the tractor enters the 7" cased and 6-1/8" open hole sections. The slim size of the tractor and expansion ratio were the main challenges to overcome in designing a tractor capable of delivering a high enough pull force to reach deeper target depths. It was recognized that a radical change in slim tractor design was required if these goals were to be met. Although 2-1/8" slim CT tractors have been used extensively in this field, the results were not always consistent, leading to reduced coverage during the acid stimulation of the well which resulted in lower production and reservoir optimization. These previous tractors relied upon wheel sections to transfer the pulling force to the casing or open hole. Although these tractors performed well in the cased hole environment, they were less effective once the wheels came in contact with the reservoir rock. To overcome this deficiency, a completely new approach was taken in designing a slim tractor that could deliver a much higher pull force with improved grip in the open hole section. The new design uses a synchronized gripper system to enable the tractor to have continuous traction in the open hole section. This new compact design, while less than ½ the length, produces almost double the pulling force of the previous wheel based slim CT tractors. During the trial test, the tractor delivered a pulling force of up to 3500 lbs to overcome friction and helical buckling forces to reach the target depth (TD). This resulted in an increase in the stimulation coverage from the original lock up depth of around 50% of the open hole, to increase the coverage to 100% of the open hole. This new design opens a window to ultimately meet the goals of improved well treatment in long horizontals resulting in better productivity and uniform flow distribution in extended reach oil wells. New generations of the tractor are planned for development with increased pull force, higher expansion ratios for larger OH sizes and also to allow real time production logging on coil tubing.