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[Introduction] The purpose of this paper is to study the influence of real "wake effect" of adjacent offshore wind farms on generation loss. [Method] The method is established with the wake scene classification based on the actual arrangement of wind farms under different wind direction and the real wake power loss of adjacent wind farms (with a spacing of more than 20D) in operation are analyzed, based on the actual SCADA data of wind turbines in large offshore wind farms and the measured wind data of LIDAR in the same period. [Result] The results show that: for the large-scale offshore wind farms with regular arrangement, the power generation normalization of the actual SCADA data can better reflect the distribution characteristics of offshore wind energy resources and the difference of power generation capacity; Under the condition of highly centralized wind direction, the adjacent wind farms in the downwind are obviously affected by the "wake effect" of the upwind wind farm; The buffer zones with different distances of adjacent wind farms have an obvious effect on the recovery of wind speed which affected the power generating capacity. The power generating capacity can be improved but if the buffer zone can reach enough distance; In different scenes of this case, the buffer zone distance is between 23D and 44D, and the power loss of wake decreases by 27%~4%. [Conclusion] This work can provide guidance for the planning of offshore wind power base and the optimization design of large offshore wind frams.

Based on the research of the formation mechanism and evolution rule of hydrate flow obstacle during deep-water gas well testing, a new method for the prevention of hydrate flow obstacle based on safety testing window is proposed by changing the previous idea of “preventing formation” to the idea of “allowing formation, preventing plugging”. The results show that the effective inner diameter of the testing tubing and the wellhead pressure decrease gradually with the formation and precipitation of hydrates during deep-water gas well testing, and it presents three typical processes of slow, fast and sudden changes. There is a safety testing window during deep-water gas well testing. The safety testing window of deep-water gas well testing decreases first and then increases with the increase of gas production rate, and increases with the increase of hydrate inhibitor concentrations. In the case with different testing production rates, a reasonable testing order with alternate low and high gas production rates has been proposed to further reduce the dosage of hydrate inhibitor and even avoid the use of hydrate inhibitors considering the decomposition and fall-off of hydrates. Compared with the traditional methods, the new method based on safety testing window can reduce the dosage of hydrate inhibitor by more than 50%.

The feasibility of gas kick early detection outside the riser was analyzed based on gas-liquid multiphase flow theory. Then an experimental platform for gas kick early detection based on Doppler ultrasonic wave was established and the propagation experiments in two-phase flow of gas-water (sucrose solutions) were conducted. The time and frequency domains of the Doppler ultrasonic wave signals during the experiments were analyzed. The results show that: (1) No matter the pump was on or off, the detected average Doppler ultrasonic signal voltage increased first and then decreased with the increase of the gas void fraction, and had a quadratic function relation with gas void fraction, so the average voltage change of the monitored signals can be used to deduce the approximate gas void fraction. The Doppler ultrasonic wave signal voltage was significantly reduced in magnitude and variation in the solution with higher viscosity, and the viscosity has stronger impact on the magnitude of signal than density. (2) When the pump was stopped, the Doppler shift increased with the increase of gas void fraction, and the two showed a nearly linear relation, so the detected amount of Doppler shift can reflect the variation of gas void fraction quantitatively. When the pump was on, the sound energy produced by frequency converter had a more significant impact on amplitude spectrum than gas void fraction, so it is impossible to determine whether gas kick occurs by frequency domain signal analysis. (3) This method is a non-contact measurement, with no contact with the drilling fluid and no disruption to the drilling operation. It can quantitatively characterize the gas void fraction according to the change of Doppler ultrasonic signal, enabling earlier detection of gas kick.

Considering the complicated interactions between temperature, pressure and hydration reaction of cement, a coupled model of temperature and pressure based on hydration kinetics during deep-water well cementing was established. The differential method was used to do the coupled numerical calculation, and the calculation results were compared with experimental and field data to verify the accuracy of the model. When the interactions between temperature, pressure and hydration reaction are considered, the calculation accuracy of the model proposed is within 5.6%, which can meet the engineering requirements. A series of numerical simulation was conducted to find out the variation pattern of temperature, pressure and hydration degree during the cement curing. The research results show that cement temperature increases dramatically as a result of the heat of cement hydration. With the development of cement gel strength, the pore pressure of cement slurry decreases gradually to even lower than the formation pressure, causing gas channeling; the transient temperature and pressure have an impact on the rate of cement hydration reaction, so cement slurry in the deeper part of wellbore has a higher rate of hydration rate as a result of the high temperature and pressure. For well cementing in deep water regions, the low temperature around seabed would slow the rate of cement hydration and thus prolong the cementing cycle.

To decrease the risk in deep water drilling and shorten the drilling period, a conductor soaking time design method for deep-water jetting was provided and verified by oil field application. Based on the field simulation experiment of soil-pile interaction, the relationship between soaking time and bearing capacity was achieved, and a real-time bearing capacity calculation model of conductor was established. The mechanical properties of conductor in two conditions were analyzed, including Cam Activated Drilling Ahead (CADA) tool releasing stage and surface casing cementing stage, and the soaking time windows of the two stages were designed. Field application results show that: This method can ensure the safety in deep water drilling, optimize driving depth of conductor, and also improve the drilling efficiency. More than 12 hours per well on average in CADA tool releasing stage and 24 hours per well on average in surface casing cementing stage were saved. Key words: deepwater drilling, conductor, jetting, soaking time, bearing capacity

In view of the absence of a theoretical model for choosing the bit stick-out in deepwater conductor jetting operation, and the existing operational blindness and risks, a bit stick-out calculation model was built up through theoretical derivation and field tests to provide the theoretical basis for the design of reasonable bit stick-out. Theoretical analysis assumes that bit stick-out is the best when the upper edge of the jet flow sprayed from the bit nozzle tip is internally tangent to the lower edge of surface conductor, based on which a formula to calculate the reasonable bit stick-out was derived, and the rationality of the theoretical assumption and correctness of calculation model were proved through field tests. Field test results show that the conductor running speed is in positive correlation with bit stick-out, while the restoration of friction between the conductor and surrounding soil body is in negative correlation with bit stick-out. The calculation model was applied in the drilling operation of 12 deepwater wells in the South China Sea and got good application effects. It saved 14.96 h per well on average, enhanced operational efficiency, and met the safety requirements at the same time. Key words: deepwater, jetting, surface conductor, bit stick-out, calculation model, field test