Study On The Formation Stress Calculation Method And Well Leak Mechanism For Aloft-steep And Complex Structure

The well leak problem in different degree occurs in all prospect area of SiChuan, especially, in the east of Sichuan. Its geologic structure is complex, and 80% structures belong to aloft-steep structure, In practical drilling process, structure is steep, formation is fragmented, fault is more, fracture and porosity are developing, pay formation is more, open hole well pressure coefficient discrepancy are great, many suite pressure system coexist, well leak is fairly frequency, complex borehole is unavoidable, and drilling and exploratory development speed are severely restricted, In order to put into effect safely rapidly drilling, well leak must overstep difficulty.Aiming at the well leak problem in drilling process, based on rock mechanics laboratory experiment and field experiment data, using finite element approach of solid mechanics and fluid mechanics, the well leak mechanization of complex aloft-steep structure is systematically studied. It is fully significant sense to promote exploratory development of oil gas in the Sichuan Basin. This dissertation was emphatically researched below 7 respects work.(1)The method to interpret rock mechanics parameter using well logging and the rock mechanics experiment are studied.(2)The method to calculate formation stress of aloft-steep structure is studied using well logging data.(3)The leak formation of complex aloft-steep structure is identified, and the property of leak channel is studied using logging data.(4)The geomechanics of complex aloft-steep structure well leak is analyzed.(5)The correlativity of complex aloft-steep structure to property of leak channel, fracture morphology and well leak are studied. (6)The rule of well leak in complex aloft-steep structure is studied.(7)The blockage mechanics mechanism of aloft- and steep structure is studied. The working capacity of the dissertation is greatly, the content is rich, and the difficulty is greatly. The innovation efforts are acquired by means of research, as following:(1)Considering the actual geology feature of complex structure of aloft- steep, a series of approaches are established to calculate formation stress magnitude and orientation accurately, and determine leak formation and channel property.(2)The geomechanics problem is analyzed to complex aloft-steep structure using the theory and method of the non-linear rock mechanics. Applying the theory of fracturing mechanics and the injury mechanics and stemming from two kinds of stress conditions such as compression and stretching shear, the injured evolution model is established at the complex crumble formation under the complex stress condition, and the mechanics mechanism of well leak is researched in complex aloft-steep fractured formation. The principle and method of rock mechanics analysis fitting complex aloft-steep fractured formation are presented.(3)Based on the rule to non-Newton fluid in fracture formation, the well leak model isestablished. Leaking process are divided into three flowing ranges, that is to say, flowing in fracture, flowing in filter cake , and flowing in formation. The analytic model is established to complex aloft- steep well leak. The influences of well leak rule are studied on the formation elements(porosity, permeability), the space of feature leak channels, construction parameter(drilling fluid density, rheological property, mud cake etc.), the mostly factors infecting well leak sensibility are analyzed, utilizing the finite element method of non-Newton fluid mechanics to research the character of flow field of fluid leak(flowing speed, pressure drop) and leak feature.Based on the feature of leak pressure profile, the blockage mechanism of fractured formation is analyzed applying fluid mechanics rule and random migration model. Uniting the distribution form in natural fracture, the propagation regular of leak pressure and strength character of blockage material are studied drilling fluid and stop water loss in fracture, the theory reference is provided for effective blockage technology and measure to fractured formation.