With the increasing demand on gas worldwide, condensate banking represents a challenging problem in tight reservoirs and can significantly impair the production rate. Gas injection and water-altering gas are the common techniques used to avoid the condensate development by maintaining the reservoir pressure above the dew point curve. However, these treatments are associated with high operational costs and large initial investment, also they are considered as temporary methods.
This study presents a chemical treatment for permanent removal of condensate banking using thermochemical fluids. Chemicals are injected to react downhole and generate in-situ pressure and heat. High pressure will raise the gas pressure above the dew point, and the generated heat will change the phase of liquid condensate to gas. The effectiveness of thermochemical treatment in mitigating the condensate damage in different types of sandstone rocks is presented. The effect of mineralogical composition on the condensate removal was investigated. Also, the impact of clay content on the efficiency of thermochemical treatment was investigated.
Results showed that thermochemical treatment is an effective method for removing the condensate damage from different types of sandstone formations. Condensate removal of more than 60% was achieved using Huff and Puff injection mode. Good correlation between the rock permeability and the condensate removal efficiency was observed. Higher condensate removal was obtained for the rock samples of high permeability values. Moreover, the presence of sensititve clay minerals in the treated rock showed miner correlation on the effectiveness of condensate removal, which indicates that the injected chemicals are able to stabilize the clay minerals and avoid clay damage. No clay swelling or particle migration was induced during the thermochemical treatment, since no permeability reduction was observed for all samples. Instead, the treated samples showed higher permeability values after the injection of thermochemical fluids. In addition, the profiles of condensate removal indicate that three cycles of thermochemical injection are sufficient for mitigating the condensate banking, and small condensate removal can be achieved during the late cycles of Huff and Puff operation.
This paper shows that thermo-chemical treatment can remove more than 60% of the condensate damage for different types of tight sandstones. Huff and Puff treatment was found to be very practical to remediate the condensate banking from different sandstone rocks. Also, this work confirms that thermo-chemical treatment can be applied in the formation with sensitive clays for removing the condensate banking without affecting the clay stability or inducing clay damage.