Igneous rock oil
and gas reservoirs have great development potential.
Hydraulic fracturing is an important means for the development of
these reservoirs. In the process of fracturing and increasing production,
fracturing fluid is prone to a hydration reaction with clay minerals
in igneous rock, and then, the structure and mechanical properties
of the igneous rock are changed, affecting increased production. Therefore,
it is necessary to establish a systematic water–rock reaction
experiment method to understand the influence of fracturing fluid
on the structure and mechanical properties of igneous rocks and to
optimize the fracturing fluid system of igneous rock reservoirs. In
this experiment, four solutions were used: slickwater, guar fracturing
fluid, 2% KCl aqueous solution, and 4% KCl aqueous solution. Acoustic
testing, porosity and permeability testing, XRD analysis, micro-CT
scanning, and displacement experiments were performed. The influence
of different fracturing fluids on the structure and mechanical properties
of igneous rocks was studied. Igneous rock samples with a permeability
of 0.05–0.1 mD and average porosity of 7–14% were used.
The results show that all four liquid systems will reduce the permeability,
Young’s modulus, and brittleness index and increase the porosity
and Poisson’s ratio of the rock after fracturing. Among them,
the permeability damage rate is as high as 37.37%, which may be related
to the plugging of pores with solid residues in the gel breaking liquid;
CT results show that there are microcracks in the rock, which increase
over time, up to 13.54%. The brittleness index decreases. Among the
fluids, the influence of slickwater on the rock brittleness index
is the smallest, no more than 5%. Guar gum had the greatest effect
on the Gel breaking liquid, up to 58%. One of the reasons for the
increase in porosity is that adding a clay stabilizer composed of
inorganic salts and organic cationic polymers to the slickwater fracturing
fluid can effectively reduce the damage caused by the fracturing fluid
to the rock during the fracturing process and can reduce the maximum
by 50%. This paper can clarify the damage law of fracturing fluid
systems to igneous rock reservoirs and provide the theoretical basis
for the hydraulic fracturing of igneous rock reservoirs.