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Wax appearance temperature (WAT) of live oil is a key index for determining the reasonable injected water temperature of high waxy oilfield. In view of the difference of the oil composition and pressure between live oil and dead oil under reservoir conditions, aiming at the practical problems such as the limitation to dead oil of the normal test method at home and abroad, based on the response of the ultrasonic parameters such as transit time, amplitude and frequency during waxy participation, a novel ultrasonic detection system used for the wax participation characteristics was designed. Taken typical oil samples of kingfisher oilfield as an example, WAT, amount of wax participated and dynamic wax participation process of both dead and live oil under different pressures were studied, respectively. Results showed that there exist two main stages for the wax participation process: nucleation and growth. The existence of the dissolved gas decreases the WAT significantly. The higher the pressure, the higher the WAT for the oil above the saturation pressure. Transit time, amplitude and frequency could all be used as sensitive parameters to estimate the WAT, amount of wax participated and dynamic wax participation process.

Experimental approach was performed in this paper to study the threshold pressure gradient (TPG) in tight gas reservoir. The nonlinear flow behavior of tight gas reservoir was investigated at first, three zones of flow curve are divided to describe the nonlinear behavior of gas flow in tight formation: solid–gas viscous force zone, slippage zone and low-speed turbulent zone. On this basis, experiments using modified procedure were made in order to clarify the influence of pore pressure on TPG, results show that TPG of tight gas reservoir is highly effected by pore pressure and conventional experimental methods will lead to a significant error. And then, TPG during the development of tight gas reservoir was tested. The results we obtained demonstrated that there exists ‘Dynamic TPG Effect’ during the development process of tight gas reservoir: TPG is increasing along with the decrease of reservoir pressure (pore pressure). New concepts of ‘TPG Rising Cone’ and ‘TPG Sensitivity Coefficient’ are defined to characterize the dynamic TPG of tight gas reservoir. Finally, experiments were carried out to investigate the influence of permeability and water saturation on dynamic TPG. Results indicate that ‘TPG Rising Cone’ is more significant in reservoir with low-permeability or high water saturation.

Wax crystallization is a serious problem because it may result in the plugging of wellbores, production facilities, and transportation pipelines during oil production. This study describes the use of a novel high-pressure ultrasonic detection system as a reliable technique to evaluate the wax appearance temperature (WAT) and the wax precipitated curve (WPC) of both crude oil [stock tank oil (STO)] and live oil at pressures up to 22.87 MPa. The oil sample was from Kingfisher (KF) oilfield, which is a typical high waxy reservoir. Transit time and amplitude were demonstrated to be good indicators for WAT determination with the ultrasonic method, which could not only self-verify but also distinguish the different stages of the complex process of wax crystallization. In addition, differential scanning calorimetry (DSC) and the rheometry method under ambient pressure were also presented to match the ultrasonic method. The obtained WAT data are comparable to results from DSC and rheometry, which could be used to...

CO 2 flooding is a proven great method to be used for enhancing injection capacity and increasing oil production in low permeability reservoir. In this paper, based on the natural cores and crude oil of Jilin oilfield, three sets of long core tests were conducted to study oil recovery, GOR and pressure variations during water flooding and CO 2 flooding. The performance of advanced CO 2 injection, simultaneous CO 2 injection and water injection were compared to optimise injection opportunity and injection pattern for low permeability reservoir. Results indicate that advanced CO 2 injection is better in maintaining reservoir pressure and improving displacement efficiency. It is considered that advanced CO 2 injection before oil production supply valuable opportunity for CO 2 to fully contact with oil which could help decrease oil viscosity and interfacial tension, swell oil volume and increase injection rate effectively.