ABSTRACT
Studying the gas-water distribution characteristics is essential in guiding the efficient development of gas fields. The relationship between gas and water in the Sudong 41-33 Block is complicated and has not been adequately researched. In recent years, gas wells have suffered from increased water/gas ratios and significant liquid loadings, which greatly affect the development of the block. A comprehensive analysis of formation water, log interpretation, and production data was conducted to determine the gas-water distribution characteristics and main controlling factors in the Sudong 41-33 Block. The findings indicate the following. (1) The formation water in the study area consists mainly of CaCl2 brine with high total dissolved solids (TDS) (with an average value of 36.06 g/L). The hydrochemical characteristics indicate that the formation water is typical sedimentary buried water under well-sealing conditions, which is markedly different from shallow river water and seawater. (2) The formation water can be categorized into three types: edge-bottom water under the gas layer (Type I), stagnant water in tight sandstone (Type II), and isolated lenticular water (Type III). The water layer distribution in the plane is mainly concentrated in the northwest region, whereas it is dispersed in other regions. On the vertical, the water layer mainly appears in P2x8-1, P2x8-2, and P1s2 Members. (3) The physical properties of the reservoir, hydrocarbon generation intensity (HGI), source rock-reservoir relationship, and mini-structure are the main factors affecting the gas-water distribution in the study area. Based on the clarification of the characteristics of gas and water distribution and its main controlling factors, it is of great importance to accurately identify the water layer, avoid the direct development of the water layer, adopt the proper production pressure differential, and carry out drainage gas production measures in time to ensure the effective development of the gas field.
ABSTRACT
Detection of cracks while at their early stages of evolution is important in health monitoring of civil structures. Review of technical literature reveals that single or sparsely distributed multiple cracks can be detected by Brillouin-scattering-based optical fiber sensor systems. In a recent study, a pre-pump-pulse Brillouin optical time-domain analysis (PPP-BOTDA) system was employed for detection of a single microcrack. Specific characteristics of the Brillouin gain spectrum, such as Brillouin frequency shift, and Brillouin gain spectrum width, were utilized in order to detect the formation and growth of microcracks with crack opening displacements as small as 25 µm. In most situations, formations of neighboring microcracks are not detected due to inherent limitations of Brillouin-based systems. In the study reported here, the capability of PPP-BOTDA for detection of two neighboring microcracks was investigated in terms of the proximity of the microcracks with respect to each other, i.e., crack spacing distance, crack opening displacement, and the spatial resolution of the PPP-BOTDA. The extent of the study pertained both to theoretical as well as experimental investigations. The concept of shape index is introduced in order to establish an analytical method for gauging the influence of the neighboring microcracks in detection and microcrack differentiation capabilities of Brillouin-based optical fiber sensor systems.
ABSTRACT
Appearance of micrometer size surface cracks is common in structural elements such as welded connections, beams, and gusset plates in bridges. Brillouin scattering-based sensors are capable of making distributed strain measurements. Pre-pump-pulse Brillouin optical time domain analysis (PPP-BOTDA) provides a centimeter-level spatial resolution, which facilitates detection and monitoring of the cracks. In the work described here, in addition to the shift in Brillouin frequency (distributed strains), change in the Brillouin gain spectrum (BGS) width is investigated for the detection and monitoring of surface micro-cracks. A theoretical analysis was undertaken in order to verify the rationality of the proposed method. The theoretical approach involved simulation of strain within a segment of the optical fiber traversing a crack and use of the simulated strain distribution in the opto-mechanical relations in order to numerically obtain the change in the BGS. Simulations revealed that the increase in crack opening displacements is associated with increase in BGS width and decrease in its peak power. Experimental results also indicated that the increases in crack opening displacements are accompanied with increases in BGS widths. However, it will be difficult to use the decrease in BGS power peak as another indicator due to practical difficulties in establishing generalized power amplitude in all the experiments. The study indicated that, in combination with the shift in Brillouin frequency, the increase in BGS width will provide a strong tool for detection and monitoring of surface micro-crack growths.