Reservoir safety, testing-string safety, and flow control are key factors that should be considered in deep-water unconsolidated sandstone gas well testing work system. Combined with the feature of testing reservoir, ...Reservoir safety, testing-string safety, and flow control are key factors that should be considered in deep-water unconsolidated sandstone gas well testing work system. Combined with the feature of testing reservoir, pipe string type and sea area, the required minimum testing flow rate during cleaning up process, as well as minimum test flow rate without hydrate generation, pipe string erosion critical production, the maximum testing flow rate without destroying sand formation and the minimum output of meeting the demand of development was analyzed;based on the above critical test flow rates, testing working system is designed. Field application showed that the designed work system effectively provided good guidance for field test operations;no sand production or hydrate generation happened during the test process;the test parameter evaluated the reservoir accurately;the safe and efficient test operation was achieved.展开更多
Drilling in any environment is challenging as it poses a challenge to drill reservoir targets without losses and minimum casing strings and is even challenging in HPHT (high pressure high temperature) environment. Sei...Drilling in any environment is challenging as it poses a challenge to drill reservoir targets without losses and minimum casing strings and is even challenging in HPHT (high pressure high temperature) environment. Seismic is the fundamental for pre-drill prognosis and completion design. The target depth prognosis is achieved through depth transformation by using seismic velocities or available velocity logs in the nearby field or block and often has varying degree of uncertainty in target depths depending upon the suitable of the velocity function used. The velocity function used could be affected due to available seismic bandwidth or structure. These uncertainties in target depths often lead to increased well costs as a result of wellbore stability issues & undesired casing strings. Most common issue faced by drillers is the target confirmation & distance to these targets ahead of bit. Vertical seismic profile (VSP) look-ahead at intermediate depths is one of the approaches to mitigate these uncertainties and drill wells safely. VSP help confirm the presence of drilling targets & also predict the depth to top of these targets. Additionally, the predicted interval velocity is used to predict the pre-pressure for next section drilling. In South China Sea, oil & gas operators face a significant risk while drilling over-pressured formations. It is therefore imperative to know the depth to top of these high pressured formations to avoid drilling directly into it and risking the well. It is also important to know the pore-pressure and mud weight for the next section to be drilled for safe drilling & with minimum casing strings [1] [2] [3]. It is more difficult to get this information in the HPHT environment due to the lack of high temperature tools [4]. Schlumberger’s proprietary QVSI*—High pressure, high temperature VSI* (Versatile Seismic Imager) has been successfully used to predict the target depth for casing landing and pore-pressure prediction in HPHT environment. QVSI is the latest generation of VSI* Versatile Seismic Imager tools developed by Schlumberger to acquire high quality tri-axial borehole seismic data in extreme environment wells. The QVSI* tool uses the Q-Technology* singlesensor hardware and software and advanced wireline telemetry for fast digital seismic data transmission from borehole to surface. QVSI is a high-temperature, high-pressure array tool design that focuses on tri-axial vector fidelity and efficient data acquisition, extending the limits in a 4-tool configuration to 500°F (260℃) and 30 kpsi (207 MPa). In this paper, a case study is presented for Well-XX for CNOOC from South China Sea. The well-xx is located in Yanyan Sag, Qiongdongnan Basin and the downhole temperature was 204℃. The main target layer is Lingshui III sandstone, which is controlled by Northwest fault. It is a gas well and critical for the client to land the casing at right depth and know the drilling parameters for the next section ahead. QVSI* predicted the target depth within ±2 m for decision on casing point. The predicted pore pressure was within ±0.1 ppg.展开更多
文摘Reservoir safety, testing-string safety, and flow control are key factors that should be considered in deep-water unconsolidated sandstone gas well testing work system. Combined with the feature of testing reservoir, pipe string type and sea area, the required minimum testing flow rate during cleaning up process, as well as minimum test flow rate without hydrate generation, pipe string erosion critical production, the maximum testing flow rate without destroying sand formation and the minimum output of meeting the demand of development was analyzed;based on the above critical test flow rates, testing working system is designed. Field application showed that the designed work system effectively provided good guidance for field test operations;no sand production or hydrate generation happened during the test process;the test parameter evaluated the reservoir accurately;the safe and efficient test operation was achieved.
文摘Drilling in any environment is challenging as it poses a challenge to drill reservoir targets without losses and minimum casing strings and is even challenging in HPHT (high pressure high temperature) environment. Seismic is the fundamental for pre-drill prognosis and completion design. The target depth prognosis is achieved through depth transformation by using seismic velocities or available velocity logs in the nearby field or block and often has varying degree of uncertainty in target depths depending upon the suitable of the velocity function used. The velocity function used could be affected due to available seismic bandwidth or structure. These uncertainties in target depths often lead to increased well costs as a result of wellbore stability issues & undesired casing strings. Most common issue faced by drillers is the target confirmation & distance to these targets ahead of bit. Vertical seismic profile (VSP) look-ahead at intermediate depths is one of the approaches to mitigate these uncertainties and drill wells safely. VSP help confirm the presence of drilling targets & also predict the depth to top of these targets. Additionally, the predicted interval velocity is used to predict the pre-pressure for next section drilling. In South China Sea, oil & gas operators face a significant risk while drilling over-pressured formations. It is therefore imperative to know the depth to top of these high pressured formations to avoid drilling directly into it and risking the well. It is also important to know the pore-pressure and mud weight for the next section to be drilled for safe drilling & with minimum casing strings [1] [2] [3]. It is more difficult to get this information in the HPHT environment due to the lack of high temperature tools [4]. Schlumberger’s proprietary QVSI*—High pressure, high temperature VSI* (Versatile Seismic Imager) has been successfully used to predict the target depth for casing landing and pore-pressure prediction in HPHT environment. QVSI is the latest generation of VSI* Versatile Seismic Imager tools developed by Schlumberger to acquire high quality tri-axial borehole seismic data in extreme environment wells. The QVSI* tool uses the Q-Technology* singlesensor hardware and software and advanced wireline telemetry for fast digital seismic data transmission from borehole to surface. QVSI is a high-temperature, high-pressure array tool design that focuses on tri-axial vector fidelity and efficient data acquisition, extending the limits in a 4-tool configuration to 500°F (260℃) and 30 kpsi (207 MPa). In this paper, a case study is presented for Well-XX for CNOOC from South China Sea. The well-xx is located in Yanyan Sag, Qiongdongnan Basin and the downhole temperature was 204℃. The main target layer is Lingshui III sandstone, which is controlled by Northwest fault. It is a gas well and critical for the client to land the casing at right depth and know the drilling parameters for the next section ahead. QVSI* predicted the target depth within ±2 m for decision on casing point. The predicted pore pressure was within ±0.1 ppg.
