ABSTRACT
The ultralow interfacial tension between the oil and aqueous phases and the solubilization characteristics in microemulsion systems make them useful for surface cleaning and enhanced oil recovery applications. Microemulsions can form an adsorbed barrier on rock, reducing the acid-rock reaction rate. However, as acid retardation additives, the adsorption patterns of microemulsions are not clearly defined. In this study, microemulsions composed of various electrical surfactants, oil cores, and oil core additives were obtained, and their phase behaviors were investigated. Through adsorption and reaction experiments, cleaning microemulsions that enhance adsorption effects were identified, and their adsorption patterns and adaptability under flow conditions were evaluated. The results demonstrate that incorporating negatively charged polar compounds forms an enhanced adsorption microemulsion characterized by an average droplet size of less than 30 nm after mixing with the acid. The introduction of negatively charged polar compounds resulted in a 177 % increase in adsorption and an 81 % improvement in static retardation effect. Dynamic adsorption tests indicate that the pseudo-second-order model more accurately describes the kinetics of dynamic adsorption of microemulsions on rock surfaces. Under a fixed flow rate, the dynamic retardation rate increased with the concentration of the microemulsion. In practical acidification, the adsorption of microemulsions results mainly from combined electrostatic forces and fluid scouring, characterized by a continuous process of adsorption and desorption. Scanning electron microscope also confirmed that microemulsions can form an adsorptive film on the rock, reducing the acid-rock reaction rate. This study offers practical guidelines for the selection and application of retardation additives, aiming to enhance the ecological compatibility of chemical treatments in low-permeability limestone reservoirs.
ABSTRACT
In the Changqing area, over 23.6% of gas wells produce less than 0.1 × 104 m3/d of gas daily, posing a challenge to gas field sustainability. Laboratory analysis of scale samples from three wells and formation water analysis via inductively coupled plasma revealed soluble salt as the primary well blockage, with sodium chloride and calcium chloride comprising 48.0-81.2% of total content. The G3# well blockage contains a small amount of quartz from acid-insoluble components of carbonate acidification. Formation water from all wells exhibited high salinity (up to 153 g/L) with a calcium chloride water type. Scanning electron microscopy and EDS confirmed halite and quartz features in blockage samples. Theoretical calculations show salt crystallization when tubing pressure falls below 10 MPa and daily water production is <1.0 tons/day. Lower production leads to lower tubing pressure and higher salt precipitation at the bottom of the well. For G1# and G2# blockages, HCl dissolves >90%, and water >85%, making them suitable removal agents. For 3# blockage, mud acid with >80% dissolution is recommended. Chemical methods effectively clean the wellbore and formation. Optimized blockage removal measures increase tubing pressure and daily production by 2.18 and 4.05 times, respectively. This study offers insights into addressing well blockage challenges in low-producing gas wells.