Characterization of Water-Rock Interaction in Water-Sensitive Tight Oil Reservoirs and its Mitigation Method with Pilot Tests

The injection of fracturing fluid into water-sensitive reservoirs can cause a rapid pressure decline during production, and the estimated ultimate recovery (EUR) of the well is only 1/4 to 1/3 of that in neighboring plays without water sensitivity. Laboratory experiments are conducted to analyze the impact of water-sensitive minerals on the rock matrix, and quantify the in-situ damage during the shut-in and production. Furthermore, water-sensitive inhibitors are developed, whose effectiveness is then examined in field pilot tests. The composition change of reservoir cores is analyzed using XRD, and their microstructure change is analyzed using SEM before and after interacting with the fracturing fluid in the mimicked reservoir condition. After water-sensitive inhibitors are developed, their effectiveness on mitigating the rock damage is characterized using the in-situ CT scans. The oil production rate and types of stabilizers of 34 oil wells in P3w1 pay zone and 29 oil wells in P3w2 pay zone are summarized. Finally the effect of stabilizer on oil production rate is investigated. The smectite ratio is over 70% in clay minerals. When the rock sample is submerged in the stabilizer solution, no clay swelling is observed. The in-situ CT scans show that the porosity decreased by 0.99% after interacting with the fracturing fluid. While when stabilizers are used in the fracturing fluid with concentration of 2%, the damage of rock permeability is reduced by 49.35%, and porosity increases by 0.66%. No obvious difference in well production is noticed when the KCl solution is used in the field. On the contrary, well production increases 40% because of the use of stabilizer. An in-situ characterization method is proposed based on a coreflood in a micro-CT, which can show the real-time change of pore structure and permeability of a rock sample. An effective water-sensitive stabilizer formula is developed, which can be a promising tool to develop water-sensitive tight oil reservoirs based on current fracturing techniques.