New Design Method of a Supersonic Steam Injection Nozzle and Its Numerical Simulation Verification.

Steam huff-n-puff in horizontal wells often had limitations, such as uneven steam injection and low reservoir utilization. To improve steam injection efficiency, a new method for designing a supersonic nozzle was proposed based on the principles of aerodynamics and thermodynamics. The nozzle featured a tapering section, a throat, and a diverging section. The best geometric shape of the tapering section was the Witoszynski curve. A set of nozzle size designs were established, and the size parameters were optimized. The results showed that the nozzle could inject steam into the formation at supersonic speed and it had the characteristics of constant flow rate and uniform development of the steam chamber. According to the steam Reynolds number and the good aggregation distribution characteristics of the size design model, three sequential nozzles of 3.0, 5.0, and 6.5 mm were formed based on the throat. When the throat diameter was 5.0 mm, the tapering length was 4.3 mm, the diverging length was 5.5 mm, the throat length was 3.0 mm, the inlet diameter was 9.8 mm, and the outlet diameter was 6.2 mm. Numerical simulations indicated that the pressure drop loss during steam huff-n-puff injection in horizontal wells was within 10%. It was of great significance to establish the nozzle size design model of the steam injection effect of horizontal wells.

Study on Hydrothermal Cracking of Heavy Oil under the Coexisting Conditions of Supercritical Water and Non-condensate Gas.

This study looked at the effects of temperature, water-oil ratio, and the addition of non-condensable gas on the thermal cracking of extra-heavy oil in the lab. The goal was to learn more about the properties and reaction rates of deep extra-heavy oil under supercritical water conditions, which are not well understood. The changes in the composition of the extra-heavy oil were analyzed with and without the presence of non-condensable gas. The reaction kinetics of the thermal cracking of extra-heavy oil were quantitatively characterized and compared between the two conditions of supercritical water alone and supercritical water mixed with non-condensable gas. The results showed that (1) under supercritical water conditions, the extra-heavy oil underwent significant thermal cracking, which led to a significant increase in the amount of light components, the release of CH4, and the formation of a new component, coke, which led to a noticeable decrease in the viscosity of the oil; (2) increasing the water-oil ratio could promote the thermal cracking of extra-heavy oil and led to a significant decrease in oil viscosity, indicating a more complete thermal cracking reaction. Moreover, increasing the water-oil ratio was found to facilitate the flowability of the cracked oil; (3) the addition of non-condensable gas intensified the conversion of coke but inhibited and slowed down the thermal cracking of asphaltene, which is detrimental to the thermal cracking of extra-heavy oil; and (4) the kinetic analysis showed that the addition of non-condensable gas resulted in a decrease in the thermal cracking rate of asphaltene, which is detrimental to the thermal cracking of heavy oil.

Macro- and Microanalysis on Noncondensable Gas Antiwater Invasion in a Bottom Water Reservoir with a Rupturable Interlayer.

Developing a bottom-water reservoir with rupturable interlayers is a significant challenge. This paper used a 2D visualization model to study the seepage characteristics of gas-water in two phases during noncondensable gas antiwater invasion. On this basis, the mechanisms of antiwater invasion and enhanced oil recovery (EOR) were summarized. The results show that bottom water advances from the crack of the interlayer to the oil layer, leading to a profile of radial flow. The major swept area occupies the scope near the horizontal well and the oil layer's middle part. Therefore, a lot of remaining oil distributes beside the crack of the interlayer. Noncondensable gas preferentially flows into the water-swept area due to a lower seepage resistance. Under gravity differentiation, the dispersed gas displaces the invaded bottom water downward, inhibiting water from invading and increasing the oil production rate. These studies provide practical guidance for analyzing bottom-water invading processes and designing suitable measures to develop such reservoirs.