Well Yuetan-1 is a high-pressure gas well in the offshore area of Liaodong Bay.During cementing of the third casing section,the Ø244.5 mm casing string was damaged and fractured at 1 238 m,which led to the sealing loss across high-pressure gas reservoir intervals from 2 626 m to 3 690 m.In order to effectively restore well integrity and meet the drilling requirements of the fourth casing section,a cement slurry system with low water loss,low flow resistance,high thixotropy and high channeling prevention capacity and thus suitable for cement squeezing operations was developed,according to the inspection results of the downhole cable camera and the downhole complex situation of Well Yuetan-1.A casing damage remedial cementing technology for high-pressure gas wells was formed,in which casing damage cracks are sealed by choke cement squeeze,and the high-pressure gas reservoirs are isolated by retainer cement squeezing and intermittent cement squeezing cement.After the treatment,the casing string was pressure-tested to 20 MPa with no pressure drop and no annular pressure,and the high-pressure gas reservoir was well sealed.The daily gas production in the trial production reached 19 000 m3/d.This technology and field application provide technical references for the treatment of similar complexities such as casing damage.
Downhole throttling can effectively prevent hydrate generation at wellhead,simplify surface processes and reduce costs.However,when this technology is applied in water-producing gas wells with ultrahigh pressure,the mutual influence between gas-liquid two-phase flow and nozzle flow may lead to significant discrepancies between the daily gas production and the designed values for some wells.Accurately predicting the flow rate and pressure drop of gas and liquid through downhole throttler is crucial to process design.To address this issue,one study was conducted based on a constructed visualization experimental apparatus to perform downhole throttling simulation experiments.The dynamics of gas-liquid two-phase nozzle flow under different flow patterns was analyzed.Data were divided based on the upstream flow pattern before the throttler,and the performance of four commonly used engineering nozzle flow models under different flow patterns was evaluated.The research results show that among the mathematical models used to predict mass and flow rate for slug flow,turbulent flow and annular flow,it is recommended to apply Ashford model(with correlation coefficient R2 is 0.92),Sachdeva model(with correlation coefficient R2 is 0.80),and Al-Safran model(with correlation coefficient R2 is 0.96),respectively.To verify the accuracy of the model evaluation results.Well Shuangtan 8 was selected for field application.The depth of the downhole throttler was determined to be 3 000 meters,the flow pattern was judged to be turbulent flow,and the calculated nozzle diameter was 5.3 mm according to the selected Sachdeva model.The evaluation results of the model can provide theoretical basis and guidance for the design of downhole throttling technology in water producing gas wells,and have certain promotion value.
Natural fractures are well developed in fractured-vuggy carbonate gas reservoirs,which are prone to lost circulation during plugging after formation testing or killing before production.Moreover,such lost circulation presents large volumes and high rates,and the complex cases of high lost circulation proneness and high difficulties in plugging,and lost circulation associated with kickoff are sometimes encountered.An integrated pipe string for formation testing-temporary plugging-production was designed,and an integrated formation test and production technology,enabled by the core tool of the pressure-controlled downhole disconnection on/off valve,was developed.With the presented technology,the reservoir can be quickly plugged by annulus pressurization;the upper pipe string can be tripped out without killing;the completion string can be tied back in clear water or low-density working fluids to connect the reservoir,which allows for production with no induced flow.Field applications showed that this technology can effectively avoid lost circulation during well killing after formation testing in fractured-vuggy carbonate gas reservoirs,significantly reduce reservoir damage,and improve recovery factor of primary production.The presented technology has excellent prospects for application promotion.
The Menggulin conglomerate reservoir is an ordinary heavy oil reservoir undergoing water flooding development.Various stimulation measures have been implemented in this reservoir,and it has now entered a high-water-cut period,showing limited potential in further increasing the recovery rate through water flooding.In order to improve the development efficiency,a field test of fire flooding was conducted.In comparison with other successful fire flooding projects in China,this block is relatively low in crude oil viscosity,porosity,and permeability,while thick in oil layer,which poses high challenges on technological processes.Therefore,based on the characteristics of an ordinary heavy oil reservoir,the fire flooding gas injection and ignition process were optimized.The commonly used four-stage gas injection process was replaced by a three-stage gas injection process,and the four-stage gradual heating ignition was simplified to one-stage heating ignition.As a result,the gas injection duration of the tubing was shortened from 3 d to 1-2 h,and the igniter temperature rose to 400℃after 19 hours of ignition.This reduced the gas injection duration of the tubing and increased the temperature rise rate during ignition,achieving safe ignition.Within three months after ignition,the oil well showed initial positive results.As of May 2023,the daily oil production had increased by 230.5%,and it is still steadily increasing,accompanied by a 16.5%decrease in overall water cut.In comparison with other fire flooding blocks,this one exhibited early and rapid response.Additionally,during the initial production stage,N2 was the main component of the produced gas,while O2 and CO2 were relatively low.The produced crude oil also showed significant improvement,with increased saturation hydrocarbon content and decreased heavy components.These findings provide valuable insights for implementing fire flooding in similar reservoirs.
Dual-layer coiled tubing drilling is a novel dual-gradient drilling technique.In order to analyze the ECD distribution characteristics in the well during dual-layer coiled tubing drilling,a computational model for calculating well ECD based on the characteristics of dual-layer coiled tubing drilling technology was developed,taking into account parameters such as well temperature,pressure and cuttings concentration.The impacts of drilling fluid displacement and density on well ECD were analyzed.The case study indicate that the well ECD increases with the increase of drilling fluid displacement and density,while slightly influenced by the increase of penetration rate.And the dimensions of the dual-layer coiled tubing need to be optimized based on the well size and circulating pressure loss.The dual-layer coiled tubing dual-gradient drilling technique can effectively reduce the bottomhole ECD,and achieve dynamic control of well pressure by adjusting drilling fluid displacement and density during drilling,providing an effective solution for addressing challenges such as narrow pressure windows in deepwater drilling and shallow leakage.
