Coupling Study On Variable-Mass-Rate Flow In Horizontal Well And Flow In Reservoir

The fluid flow in wellbore is interacted with the fluid flow in reservoir when horizontal well produces oil. A reasonable description of flow performance and pressure drop relationship in wellbore is significant to optimize wellbore length and predict the well productivity. Although a lot of researches have been done on variable-mass-flow in horizontal well, which present all parameters cause to pressure drop in wellbore, but generally some empirical correlations are got and they are restricted to use. On the aspect of coupling flow with reservoir, only frictional pressure drop in wellbore is considered just for convenience, acceleration pressure drop and inflow effects are ignored. Hence, a comprehensive coupling model considering all pressure drops is necessary. Considering different completions and different reservoir conditions, the 3D steady-state reservoir coupling open-hole completion wellbore model, the 3D steady-state reservoir coupling perforation completion wellbore model and the 3D transient reservoir coupling wellbore model are developed. These models are semi-analytical, the corresponding computational programs are done, and some actual examples are calculated. In open-well completion model, a method to calculate the mixture pressure drop along well is given, friction, acceleration and mixture pressure drops are considered in wellbore model , as well as the effect of fluid inflow into the well. According to present model, the pressure profile and flux distribution along wellbore are calculated; Comparing to infinite-conductivity well model, the coupling model shows that an optimized length for horizontal well exists, and the effect of wellbore pressure drop on well productivity should be considered, especially for long horizontal well. In perforation completion model, the model developed by Liu Xiang-ping is improved; each wellbore segment can have several perforations, so it is convenient. A new empirical apparent friction factor correlation is also used for wellbore flow computations, wall fiction and perforation friction caused by influx from perforations are considered; According to present model, some effect factors, for example, perforation length, perforation density and phase angle on well productivity are analyzed, perforation length is the dominant parameters controlling the productivity, the phase angle and perforation shot density have been shown to have secondary effect, and perforation density has an optimum value.Besides, based on transient flow theory and boundary integral method, a new transient coupling model of horizontal wells is proposed to study the performance of horizontal well at any time. The computational program is done to calculate the actual example, flux distribution at different time is presented, and profiles of friction and acceleration pressure drops are analyzed. All these models are flexible and they can provide advanced methods to study variable-mass-flow in horizontal well under different conditions.