Gao, Jichao (China Oilfield Services Limited) | Feng, Puyong (China Oilfield Services Limited) | Wang, Da (China Oilfield Services Limited) | Shao, Shangqi (China Oilfield Services Limited) | Cui, Bo (China Oilfield Services Limited) | Wang, Gui (China Oilfield Services Limited)
Matrix acidizing is widely used for removing damage of carbonate reservoirs. In 2017, more than 70 matrix stimulation operations have been conducted in Iraq Missan oilfield. However, for wells with no severe damage and low production performance which are influenced by formation energy decreasing, the effect of conventional matrix is limited. In order to stimulate these wells, a new acidizing technique has been developed which is called large liquid volume deep penetration acidizing.
According to the Darcy Productivity Equation, for carbonate reservoir, decreasing the skin factor below 0 would also increase production even if the skin factor is 0. That is the theoretical basis of large liquid volume deep penetration acidizing. The key points of this method are injection volume and acid system characters. Total injection volume is even twice as large as that of conventional matrix acidification. The acid system should have characteristics such as retarded acid-rock reaction rate and low leakoff coefficient. Viscoelastic surfactant based acid PA-VES and gelled acid PA-GL are used in these works.
In high permeability formation, the viscosity of PA-VES [20 wt% HCL and 8 wt% VES-1] reaches a peak of more than 400 cp at a shear rate of 170 S−1 at 120°C, which would drive acid flowing into tight formation. Other characteristics such as corrosion inhibition, surface tension, inter-surface tension, iron control and sludge prevention have been tested. Gelled acid is widely used because of its economic benefit, its rheology behavior is tested too. During injecting procedure, optimizing the injection rate and choosing large acid volume to produce long effective wormhole in formation, in this way the oil and gas seepage resistance are reduced, deep oil and gas reservoir area is connected, and oil production is improved. 3 wells have been stimulated using this technique in Missan oilfield which achieved the good results.
Large liquid volume deep penetration acidizing still belong to matrix acidizing because of non-fracturing formation. So that this method do not need a rig and would save cost. This paper introduces a novel method to stimulate low formation energy wells and low pollution wells, which is used in Iraq Missan oilfield for the first time.