Applying statistical and oilfield methods in predicting waterflood induced hydraulic fractures in the injection wells

UDK: 622.276.432
Key words: injection wells, waterflood induced hydraulic fracture, fracture initiated by injection, minimum principal horizontal stress, falloff test
Authors: A.I. Shchekin, E.N. Grishchenko, Sh.R. Lotfullin, A.S. Klevtsov (Vietsovpetro JV (Vietsovpetro JV, the Socialist Republic Vietnam, Vung Tau), A.A. Lubnin (Zarubezhneft JSC, RF, Moscow)

Currently, there is loss of flooding efficiency due to premature inundation of production wells in the Vietsovpetro JV, when new areas related to the Lower Miocene sediments begin to be developed in the block 09-1 offshore fields in Vietnam. A detailed analysis of the causes of inundation wells shows that in addition to water filtering which is pumped into highly permeable streaks, the main aggravating factor is formation of waterflood induced hydraulic fractures in the injection wells (fracture initiated by injection). In order to improve the efficiency of water flooding system in the oilfields of Vietsovpetro JV the issues of identifying and predicting the formation of w-induced hydraulic fractures were analyzed using statistical and field research data of the wells.

Using actual mini-frac data and reservoir pressure measurements in production wells on the Block 09-1 offshore Vietnam, the statistical dependence was designed to evaluate the initial minimum principal horizontal stress (pressure of fracturing initiated by injection). Verification of established dependence was performed by comparing the calculated values of pressure of fracture initiated by injection with the actual data, obtained as a result of hydrodynamic research of injection wells at steady state regime.

the analysis of changes of the minimum principal horizontal stress, based on the data of falloff test in injection wells with waterflood induced hydraulic fracture, was performed to study the possibility of control the development of cracks and to prevent its re-opening. It was determined that under the influence of periodic regime of the injection wells within conditions when bottom hole pressure exceeds the pressure of fracture initiated by injection, the considerable modification of the stress-strain state of the formation takes place. This accompanies with decrease of the minimal principal horizontal stress values, which increases the risk of uncontrolled crack growth and premature inundation of wells.
References
1. Afanas'eva A.V., Gorbunov A.T., Shustef N.N., Zavodnenie neftyanykh
mestorozhdeniy pri vysokikh davleniyakh nagnetaniya (Water flooding of oil
fields at high injection pressure), Moscow: Nedra Publ., 1975, 215 p.
2. Zoback M.D., Reservoir geomechanics, Cambridge University Press, 2007,
504 p.
3. Ching H.Y., Mechanics of hydraulic fracturing, Gulf Publishing Company,
1997, 182 p.


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