Increasing the stimulation efficiency of heterogeneous carbonate reservoirs by developing a multi-bached acid system

Abstract

Matrix acidizing is a common practice in the oilfield for minimizing formation damage through dissolution of the reservoir rocks and making appropriate wormholes. For obtaining the highest performance in the acidizing and stimulation treatments, the injecting fluid should be placed in the damaged zones of the reservoir layers, after which the easy flowback could fully improve the formation damage. In multi-layered oil reservoirs the fluid diversion becomes of paramount importance where preferential flow paths are adopted in most of the stimulation fluid and the zones, which have the lower values of the rock permeability, remain untreated.We develop an optimal multi-bached acid system in two steps by determining the diverter formulation and investigating the diverting characteristics of the acid system through core flood tests. The interfacial tension tests were conducted to determine the diverter (fluid packer) formulation. The effects of different concentrations and mixtures of organic acids, HCL and surfactant were investigated to find the most effective main batch (active batch) of the stimulation fluids. In the second experimental phase, the ability of the selected emulsified acid system as a fluid packer and diverter was investigated using the multi-bached acid system in a parallel core flood test. The results showed the efficiency of the emulsified acid system in diverting the second batch (active batch) of the stimulation fluid from the core with the higher permeability to the lower permeability one.We find that the developed multi-batch acid stimulation system is an advantageous technique to use for stimulating the multilayered wells where there is a big difference between the permeabilities of the producing formations. The permeablity improvement in a more uniform manner in both the layers proves the efficiency of the developed stimulation system and emulsion which used as a diverter. In addition, we detect that the mixture of 15%HCL and surfactant (GF – 15 MPS) with 0.5% concentration has provides the optimal reaction rate and dissolution rate in comparison with other mixtures studied by increasing the neutralization time.In short, firstly, in this work the acid distribution rate mechanism (pathway) between the reservoir layers was investigated by simulating the executed actual matrix acidizing operation in the considered well. Then, The self-diverting emulsified acid SDEA (which can be used as a diverter) was developed. Moreover, the main batch of stimulation fluid was developed by analyzing different acid mixtures with various concentrations. Lastly, the efficiency of the developed multi-bached acid system was evaluated by conducting the core-flood experiment. The results show that the developed multi-batch acid stimulation system is significantly efficient for stimulation of the heterogeneous carbonate reservoirs where there is a big difference between the permeabilities of the producing formations so that the stimulation of both layers (with different permeability values) can be accomplished in a more uniform manner.