Search

To solve the problem of poor fracture identifying effect on electrical logging in oil-based mud, the application of acoustic logging to the quantitative characterisation of fractures is expanded from three aspects, namely, Stoneley waves, longitudinal and transverse waves and cross dipole acoustic waves, and a fracture logging evaluation model closely related to production capacity is established considering the radial extension characteristics of fractures. The Stoneley reflection coefficient is used to determine fractures locations to help detect fractures during normal micro-resistivity imaging logging. Based on the experiment on the relationship between fracture width and acoustic attenuation coefficient, empirical formulae for calculating fracture width have been established by primary wave and shear wave energy information considering the effect of porosity. The new parameters, including spectrum correlation coefficient and energy difference from cross dipole array acoustic logging data, can be used for fractures evaluation. The more developed the fractures are, the greater the energy difference becomes, and the smaller the spectrum correlation coefficient is, the higher the production is. The fracture effective evaluation parameters can be separated into two components, specified as the degree of fracture vertical opening and radial extension. Combining the conventional logging and array acoustic logging (including cross dipole array acoustic logging), a fracture radial extension evaluation model is presented closely related to productivity. Key words: tight sandstone reservoir, fracture evaluation, acoustic logging, oil-based mud, radial extension, Kuqa, Tarim Basin

A new method of cement bond quality evaluation was proposed by combining numerical simulation and calibrated cased hole acoustic logging data. The effects of the cement channel angle and the quality of the second bond interface (the interface of cement with formation) on acoustic variable density logging data were analyzed. Based on the analysis result, a new cement bond evaluation standard was presented after revising the traditional CBL/VDL method. The axisymmetric acoustic field was simulated by real axis integral method, while the non-axisymmetric acoustic field was simulated by 2.5-D finite differential method. After comparing with the calibrated cased hole acoustic logging data, the research has the below results: the numerical simulation result matches with the calibrated well logging data very well and the new method is reliable; the amplitude of the first acoustic arrival in the case hole decreases as the angle of cement channel decreases, and the denser the cement is, the faster the amplitude of cased hole acoustic waveform decays; the lower limit of cement channel angle is around 45 degrees which can be detected by acoustic logging; the formation acoustic waveform is not easy to be detected in time domain, however it is easy to be detected in frequency domain, especially in limestone formation, the first arrival only can be detected when the annulus width of the second bond interface is small. According to the research result of the numerical simulation of cased hole acoustic field and acoustic variable density logging data, new evaluation criteria of cement bound quality were presented. Key words: cement bond quality, acoustic variable density logging, acoustic field in cased well, cement channel angel, interface bond index

Geological features, such as deep and thin reservoirs and unstable structure margin, occur in an oilfield of the Tarim Basin. To deal with these problems while drilling, a rotary geosteering drilling technique was introduced. The effect of its application was analyzed with an example, the shortcomings were summarized, and suggestions were given for other oilfileds. The feasibility and necessity of using rotary geosteering drilling were presented according to the engineering challenges in the oilfield, then the theory and main tools of it were introduced. Focusing on a double-step horizontal well in field application, the features and effects of this technique were elaborated. With rotary geosteering drilling in this well, the average rate of penetration was high and oil reservoir encountering rate was up to 82% in thin layers less than 1 m. Also, it avoided effortless weight on bit in sliding drilling method and made the wellbore more smooth and clean. The problems met were concluded, for example, the tools build-up rate was affected by several factors, measurement while drilling (MWD) signal was interfered, and the tools working performance was unstable. Suggestions were put forward for applying the rotary geosteering drilling technique in other oilfields. Key words: horizontal well, drilling, rotary geosteering, deep thin reservoir, logging while drilling (LWD)