Kaolinite Effects on Injectivity Impairment: Field Evidence and Laboratory Results

Summary Clay interaction with fluids is a well-known phenomenon that depends on formation mineralogy. This paper focuses on the impact of kaolinite clay dispersion on well injectivity impairment. It is based on field evidence from more than 50 injectors, and it is supported by a huge set of laboratory tests. All analyzed wells showed an initial injectivity lower than the theoretical potential, estimated on the basis of reservoir quality and drawdown mobilities (DDMs). This impairment occurs before connecting wells to the injection network; therefore, injected water quality and network conditions do not take part in the damage. Consequently, the impairment mechanism seems to be correlated to the interaction between the formation and drilling fluids. A set of laboratory experiments was planned on cuttings collected in two recently drilled wells. Different intervals were selected in the reservoir sandstones, representative of the facies where injected water is most likely to flow. Samples were first mineralogically characterized by different laboratory techniques: Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction, and cation exchange capacity. Then, swelling and recovery tests were performed using different fluids: mud (field formulation), mud filtrate, and water (varying pH and salinity). Results were correlated with petrophysical analysis, mercury injection tests on cores, and major injectivity impairments observed on the analyzed wells. Analyzed samples showed the presence of kaolinite that may affect the formation permeability by filling porosity and pore throats (diagenetic effect). Moreover, in case of interaction with fluids, kaolinite can lead to an additional permeability reduction by disaggregation and dispersion phenomena. Laboratory tests showed a clear trend: The higher the kaolinite content is in the selected intervals, the higher the observed disaggregation will be, especially when the samples interact with mud filtrate and water. It was observed that mud formulation is effective, allowing to preserve disaggregation, but only below a threshold of kaolinite content. Field experience proved that the only effective remedial actions to restore the well injectivity potential are fracturing jobs, allowing bypass of the near-wellbore damaged zone.