Kaolinite Effects on Injectivity Impairment: Field Evidence & Laboratory Results

Abstract

Abstract 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 50+ injectors and it is supported by a huge set of laboratory tests. All analysed wells showed an initial injectivity lower than the theoretical potential, estimated on the base of reservoir quality and draw-down mobilities. This impairment occurs before connecting wells to the injection network, therefore injected water quality and network conditions do not take part in the damaging. Consequently, the impairment mechanism seems to be correlated to the interaction between 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 (FT-IR, XRD and CEC). 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 analysed wells. Analysed 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 in the selected intervals, the higher the observed disaggregation, especially when 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 frac jobs, allowing to bypass the near wellbore damaged zone.