Experimental study on influencing factors of acid-fracturing effect for carbonate reservoirs

Abstract

Abstract： ： ： ：Acid fracturing treatment is the key technique for stimulation and stable production in carbonate reservoirs. In order to improve the carbonate reservoirs acid fracturing effect, in this paper, with a large number of experiments as the main research methods，study on influencing factors of acid-fracturing effect for carbonate reservoirs from increase the effective distance of living acid, increase acid corrosion eched fracture conductivity, reduce the acid fluid loss, etc. The effective distances of live acid calculated with reacted acid limitations measured in different acid systems are quite different from those calculated according to previous standard. Fracture conductivity is one of the key parameters that affects acid fracturing effects, but it's difficult to be predicted accurately due to the strong randomness of acid-rock reaction as well as various influence factors. Analyses of the impacts on fracture conductivity resulted from the rock embedment intensity, closure stress, acid dosage, rock-acid contact time, acid fluid loss, acid pumping rate through self-developed small-core fracture capacity test instrument. Fluid loss during acid fracture can be well controlled bythickened liquid as well as solid particles, but formation damage occurs inevitably. Foamed acid is a specific fluid with high viscosity, low fluid loss, small friction resistance, good retarding property, strong fracture making ability, easy flowback and low damage, which is an ideal acid system for low pressure and low permeability carbonate reservoirs. In this paper, the theoretical study on percolation mechanism and fluid-loss control mechanism of foam (acid) in porous medium are presented with the help of visual microscopic model fluid drive unit.

Development and application of a double action acidic emulsion for improved oil well performance: laboratory tests and field trials

“…This non-uniform coverage of acid in the reservoir could lead to the overall unsuccessful acidizing. Therefore, the Emulsion A, which has viscosity of approximately 50 cp could enhance the zonal coverage, sweep efficiency and acid distribution in heterogeneous reservoirs [24][25][26].…”

Assessment of oil-producing wells by means of stimulation approach through matrix acidizing: a case study in the Azraq region

“…Its purpose is dissolving sediments to reinforce rock permeability and the establishment of a clean zone within the reservoir, thus eliminating the restrictions for oil flux into the wellbore zone. Commonly, matrix acidizing is applied in case of tighter carbonate and sandstone formations; it is recommended in industry to utilize acids with mass concentrations, in the range of 10-15%, while acid fracturing is implemented in case of carbonate formations (Bale et al 2010;Li et al 2015;Liang et al 2017;Kolin et al and Kurevija et al 2018) with relatively higher acid mass concentrations, in the range of 20-30%. This method involves acid injection to create channels or so-called wormholes, as the resulting rock fractures, under pressure from the hydrocarbons, might immigrate through.…”

“…The particulate materials that are plugging the pore structure will be reducing the rock permeability extensively. In the studies of Li et al (2015), Wilfred and Umeleuma (2015), and Yancheng et al (2017), the effect of rock type, acidizing additives, and other experimental parameters were investigated on crack distributions for reservoir's rocks. Particularly, their experimental procedures widely vary and produce very different results of the treatment processes due to rock impurities.…”

An experimental study of acidizing operation performances on the wellbore productivity index enhancement

“…However, conductivity property of the fractures plays the substantial role in the acid fracturing, regarding the random reactions between rock and acid, and this phenomenon might be difficult to estimate. The factors that would seriously affect this issue are pumping rate of the acid, sufficient length of acidizing propagation, the contact time between acid and rock, closure stress and fluid loss of the acid, etc, and these significant parameters are (Li et al 2015) shown in Fig. 1 specifically.…”

“…One of the useful types of acid which is used in these reservoirs is the foamed acid with the immense value of viscosity, low rate of fluid loss, retarding agent property for deep wells and etc. (Chengshou et al 2010;Fufeng et al 2008;Li et al 2015). Mozaffari et al (2015) proposed that other factors which significantly affect the production rate in fractured carbonated reservoirs are the capillary force of liquid in microand nano-sized channels which might be blocked by the asphaltene.…”