Acid-Fracturing Techniques as a Good Alternative to Help Improve Field Development Assets

Abstract

Acidizing and acid fracturing techniques are routinely used in two important formations in the marine regions of Mexico, the Jurassic and Cretaceous formations. These formations are naturally fractured carbonate and dolomite reservoirs having a permeability in the range of 0.19 to 22 mD, porosity from 2.8 to 6%, approximate bottomhole temperature (BHT) up to 177°C, pressure (BHP) of 10,374 psi, and a crude of 45° API. Using acid fracturing techniques helps improve the development of these assets. This paper shows the results of more than 40 acid fracturing operations performed in recent years. Depending on the productivity evaluation, wells belonging to these assets are stimulated as part of the completion stage. Because of their low permeability, a common approach is to perform an acid fracturing operation. As a first evaluation, a minifrac test is executed to obtain the necessary data to calibrate the acid fracturing simulation model. After this step is performed, the acid fracturing design is evaluated. Generally, a sustained production acidizing technique is used for conductivity enhancement and closed-fracture acidizing is also included as a tailored treatment with an all seawater-based acidizing system. For these operations, an average five-fold increase in oil production has been observed after treatment. In some cases wells in the completion stage, having no production before treatment, delivered up to 7000 BOPD after treatment. In these low-permeability assets, the post-fracturing response shows good results in general terms, increasing final conductivity in the near-wellbore area, and improving the production in these wells. The fracture gradient observed varies from 0.715 to 0.981 psi/ft with an average minimum stress of 13,670 psi. To perform the acid fracturing treatments, an average of 6400 hydraulic horsepower (HHP) must be available, with up to 13,400-psi surface pressure observed. As such, a stimulation vessel is necessary in all operations, applying a 26-bbl/min average pumping rate. Globally, acid fracturing treatments are a common stimulation technique. This study shows that stimulating proper candidates in Mexico using acid fracturing significantly helps increase production, which may be relevant for the exploitation of new areas where fracturing has not been implemented.

Study on Optimization of Stimulation Technology of Heterogeneous Porous Carbonate Reservoir

“…Subsequently, acid fluid is injected into the formation. Because the viscosity of the pad fluid is higher than that of the acid fluid, the acid fluid will produce "fingering" during the displacement of the fracturing fluid, which helps the acid fluid to carry out non-uniform etching on the fracture wall [29,30]. Alternate injection of pad fluid and acid fluid will reduce the filtration rate of subsequent injection of acid fluid.…”

“…higher than that of the acid fluid, the acid fluid will produce "fingerin placement of the fracturing fluid, which helps the acid fluid to carry etching on the fracture wall [29,30]. Alternate injection of pad fluid a reduce the filtration rate of subsequent injection of acid fluid.…”

Effect of Acid-Injection Mode on Conductivity for Acid-Fracturing Stimulation in Ultra-Deep Tight Carbonate Reservoirs

“…The frequently used acid systems include gelling acid and crosslinked acid, which are mainly applied for etching hydraulic fractures and generating conductivity. This injection mode is straightforward to implement on-site and extensively utilized in the initial stages of acid-fracturing development [13,14]. Multistage alternating acid fracturing is an enhanced mode of pre-pad acid fracturing, employing alternate stages of pad fluid and acid.…”