An Insight Into Development of Bottom Water Reservoirs

Abstract

While water production is an inevitable consequence in bottom water reservoirs, it is usually desirable to defer the onset or the rise of water coning as long as possible. Numerous mechanical and chemical methods have been applied to achieve this goal over recent decades. This paper presents new insights into improving oil production and reducing water production by considering flow barriers below horizontal well trajectories in formation regions with low permeabilities, especially natural ones such as shale bodies. A 3D numerical simulation that applies the Computer Modelling Group's (CMG) STARS Simulator as a cost-effective way to investigate the effects of barriers on horizontal well performance in a bottom water reservoir has been conducted. More specifically, the effects of permeability, dimension, and position of barriers have been comprehensively analyzed when a horizontal well is implemented as a producer. The simulation results have shown that if barriers exist below a horizontal producer, water cut can be postponed and reduced greatly, and cumulative oil production can be increased. Cumulative water production can be decreased dramatically as well. To broaden the applicability of this new insight, some of the possible field implementing technologies, including fractured horizontal wells, small-scale CO2 injection, and solvent injection, are qualitatively simulated to determine their applicability for developing heavy oil in bottom water reservoirs using horizontal wells with the presence of barriers. The simulation results have shown that much better well performance can be reached with the help of barriers when these technologies are integrated systematically. This new strategy shows a rather promising and economic way to develop bottom water reservoirs where the natural driving energy of the aquifer could benefit the oil production process. The results and understanding acquired from this study offer insights into the development of bottom water reservoirs. Introduction Water coning is a critical issue for conventional vertical well production in bottom water reservoirs. Generally speaking, the fluid production process creates a low-pressure region around the wellbore in the reservoir. This differential pressure causes the oilwater interface to deform into a cone shape, at which time the less viscous water phase is produced in preference to the more viscous oil phase. Consequently, the producing Water-Oil Ratio (WOR) increases quickly and readily reaches an uneconomic level. Darcy's law is still the fundamental principle behind this phenomenon. In the past, many researchers have conducted experimental, analytical, and numerical studies on water coning behaviour in vertical wells. Muskat and Wyckoff(1) published one of the early studies related to water coning in 1935. They observed that water coning is a rate-sensitive process and determined the critical oil rate, which is the maximum water-free production rate, by neglecting the shape of the cone. Later on, researchers(2, 3) directed their studies toward the calculation of the critical oil rate. Guo and Lee(4) indicated that the critical rate does not occur at zero wellbore penetration, as may intuitively be expected, but at a wellbore penetration of about one-third of the total oil-zone thickness for an isotropic reservoir.

Numerical Simulation of Nitrogen Foam Injection to Control Water Cresting by Bilateral Horizontal Well in Bottom Water Reservoir

“…As can be seen in this figure, for IFLB, after foam injection, water invasion is suppressed significantly and foam forms strong blockage around the injection well, which can force the following water to bypass the foam zone. This phenomenon is quite similar with the simulation results obtained by Zhao et al [12]. In their simulations, when barrier exists, invasion was forced sideways and bypassed the barrier to form secondary cones along the barrier edges.…”

“…These barriers give more resistance to water invasion, so the rise speed of water cut will slow down and the well performance with respect to oil production could be much better. Many publications related to the effect of impermeable barriers on the development of bottom water reservoirs are available [12][13][14].…”

A new mathematical model for horizontal wells with variable density perforation completion in bottom water reservoirs

“…Taking China for example, there exist a large number of bottom water reservoirs, most of which are developed using horizontal wells. Compared with vertical wells, the producing sections of horizontal wells have direct contact with oil reservoirs, which not only reduces the producing pressure drawdown, but also ensures bottom water flowing into the wellbore more smoothly in a form of ''pushing upward'' (Besson and Aquitaine 1990;Dou et al 1999;Permadi et al 1996;Zhao et al 2006). Owing to these advantages, it can effectively control bottom water cresting.…”

The Effect of Interlayer on Water Cut Rise in a Bottom Water Reservoir

“…Based on the numerical simulation method, Zheng et al analyzed the influence of interlayer permeability, interlayer size, and interlayer location on the development effect of the bottom water reservoir [3]. Zhao et al used a numerical model to study the influence of permeability, size, and distribution of the interlayer on bottom water reservoir development [4]. It is considered that the water breakthrough time and productivity of horizontal wells do not increase monotonously with the decrease in interlayer permeability.…”