Managed Induced Fracturing Improves Waterflood Performance in South Oman

Abstract

Novel modelling technologies that includes induced fractures in a dynamic reservoir simulator has been used to analyse subsurface aspects of an inverted 5-spot injection pilot. The techniques have allowed an accurate depiction of growing induced fractures. Simulation results indicate that induced fracture growth is limited at injection rates < 200 m3/d but that higher injection rates will result in fracture propagation and a risk of rapid water breakthrough. The results have been validated by field observations. A controlled and cautious increase in injection rate has resulted in a positive production response with rate increases of 50–100% in three of the four producers in the pilot. Results from the pilot have increased the current reservoir understanding and reduced subsurface uncertainties. The knowledge gained is being included in an updated Field Development Plan that will be issued in 2005. The plan will incorporate an optimised injection strategy by a careful and controlled ramp up in injection rate. This project has also advanced induced fracture research with a field verification of the predictive capabilities of the modelling technology. Introduction The Marmul Haima West sandstone reservoir in South Oman, containing heavy and viscous crude (22 ºAPI, μo = 90 cP) and on production since 1980, was initially developed on depletion/solution gas drive using vertical wells. To boost production and improve recovery, an aggressive waterflood development using horizontal wells was initiated in 1999. The development was, however, stopped prematurely in 2000 after excessive induced fracture growth resulted in water short-circuiting and poor well performances. To improve subsurface understanding and redefine a development strategy, an inverted 5-spot produced water injection pilot project was initiated in 2002 with the procurement and construction of dedicated water cleaning and injection facilities and drilling of 5 new vertical pilot wells (i.e. wells I-1, P-1, P-2, P-3 and P-4). A map of the field and the placement of the 5-spot pilot have been shown in Figure 1.

Effective Well and Reservoir Management Reverses Production Decline in a Major Brownfield in South Oman

“…In view of this fact, performance of individual patterns was optimized by fixing the optimum injection rate based on step rate test 6 wherever available, plot of well-head injection rate and well-head injection pressure and Hall's plot 7 for individual injectors. The well-head injection pressures at which induced fractures were created was found to be consistent with geomechanical measurements carried out on core samples and the findings of a detailed pilot study 5 . Fig.6.…”

“…A few examples of successful implementation of recommendations from integrated pattern and well reviews are presented below: Injection Optimization: The case study has been presented in detail in literature 4,5 . During a development phase of the field using horizontal injectors and horizontal producers, the water injection in horizontal wells was initially kept at very high levels (1500-2000 m 3 /d) in order to achieve voidage replacement through a few wells only.…”

Modelling High Rate Fractured Injection in the Bonga Field

“…Modelling using PWRI-FRAC tool is a simple and fast method of analyzing induced fracture behaviour in the Bonga field, and is fit-for-purpose for complementing routine Well and Reservoir Management 10 . Pressure Transient Analysis (PTA) from IFO data is a pre-requisite to fracture modelling work in order to better understand injector performance.…”

Influence of Mineral Composition on Initiation Pressure of Waterflood-Induced Fractures in Tight Sandstone Reservoir

“…The waterflooding technique has been most widely applied in tight sandstone reservoirs. However, due to the small pore-throat radius and complex pore-throat structures, the waterflood-induced fractures (WIFs) will be generated during the long-term water-flooding process in tight reservoirs. − WIFs are the strongest heterogeneous characteristics in tight sandstone reservoirs during the middle and high water cut stage, essentially categorized as dynamic fractures . Meanwhile, the WIFs have two side effects during the water-flooding development in tight oil reservoirs, i.e., the WIFs can significantly improve the formation permeability and water injection capacity; however, it can also exacerbate the reservoir heterogeneity as the dominant seepage channel .…”