Field Studies of Spontaneous Growth of Induced Fractures in Injection Wells

Abstract

Development of low-permeability reservoirs (less than 1 mD) is carried out with intensive flooding. Injection is performed at pressure above the formation fracturing pressure that is why in almost every well a spontaneous growth of (injection) induced fractures takes place.The main problem of pressure transient analysis in a low permeability reservoir with spontaneous fracturing is a long linear regime flow observed in the log-log plot and the absence of a basis to achieve a pseudo-radial flow. To increase the accuracy of well testing in spontaneously fractured injection wells, certain field tests were developed and run. While testing, an injection well with spontaneously induced fractures was shut-in before the bottom-hole pressure went below the fracture closing pressure, then injection resumed for a short period of time, and then the well was shut-in again to record the pressure fall-off curve. The second pressure fall-off curve shows that the pseudo-radial flow developed, because the close of the part of the fracture without proppant occurred.The paper shows field examples of interference well tests exhibiting fracture growth up to 1700 m diagnosed in injection wells. Examples of successful restriction of injection well operation and application of correlation relationships of fracture closing pressure vs. formation pressure to lower water-cut in production wells with water breakthroughs are described.

Examples of Mini-Frac Test Data Interpretation in Low-Permeability Reservoir

“…al., 2010 and2014] correlation relationship between fracture closure pressure and reservoir pressure is given. al., 2010 and2014] correlation relationship between fracture closure pressure and reservoir pressure is given.…”

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 .…”

“…The identification and monitoring methods of WIFs include Hall plot analysis and its derivatives, − skin factor, injectivity index tests, water injection indication curves, water absorption profile tests, water-flooding front tests, production dynamic analysis, well testing, − interwell connectivity, , and tracer test, as shown below in Table .…”

“…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 . The main manifestations of WIFs in the oilfield are (1) the significant decrease in daily oil production and increase in water cut when the daily fluid production increases during the production process; (2) injection well shows prominent linear flow characteristics without hydraulic fracturing; (3) the water absorption profile test shows the spike-like absorption; and (4) the tracer testing in injection Wells has the obvious directionality. Currently, the research on WIFs mainly focuses on four aspects: the production mechanism of WIFs, numerical simulation of WIFs, identification and inversion of WIFs, and experimental study on WIFs.…”