Study on Wellbore Stability of Shallow Sediments in Deepwater Drilling
Method: In this paper, the shallow formation around the borehole is divided into plastic zone and elastic zone considering it under nonuniform in-situ stress. The collapse pressure formula of shallow formation is derived by taking the shrinkage rate of the borehole as the instability criterion. The fracturing pressure calculation model of shallow sediment under non-uniform in-situ stress is derived by combining the theory of excess pore pressure and hydraulic fracturing.
Prediction and Optimization of Stability Parameters of Borehole Sensor for Deep Water Drilling Based on Genetic Algorithm
In order to study the prediction and optimization of borehole stability parameters in deepwater drilling based on genetic algorithm. First, a genetic hybrid algorithm based on pattern search is proposed. Then, based on the adaptive genetic algorithm, the evolutionary population is searched for patterns, which makes the hybrid algorithm not only has a strong global search ability but also improves the local optimization accuracy. Finally, the unit footage cost in the drilling process is taken as the objective function, and the algorithm is verified by taking the drilling in Karamay area as an example. The calculation results show that if the bit wear reaches 0.8-0.9 and then the bit is pulled out, the utilization rate of the bit can be increased, the design efficiency and accuracy can be improved, and the drilling cost can be reduced. The wear amount of the optimized bit is higher than that of the actual bit. Increasing the utilization rate of the bit can reduce the cost of drilling meters to a certain extent and improve the economic benefits of drilling. The objective function and constraint conditions for the optimization of drilling parameters are determined, and the algorithm is verified with the drilling data of Karamay Oilfield. The results show that the algorithm improves the stability and speed of iterative convergence and improves the reliability of data analysis results. Based on the regional three-dimensional formation rock parameter data volume, the optimization method can be used to optimize the drilling parameters before drilling and provide a basis for formulating the drilling design scheme.
Definitions of efficiency
This is the third in a series of occasional notes on economics

Decision makers are increasingly faced with the challenge of reconciling growing demand for health care services with available funds.1 Economists argue that the achievement of (greater) efficiency from scarce resources should be a major criterion for priority setting. This note examines three concepts of efficiency: technical, productive, and allocative.

Efficiency measures whether healthcare resources are being used to get the best value for money.1 Health care can be seen an intermediate product, in the sense of being a means to the end of improved health. Efficiency is concerned with the relation between resource inputs (costs, in the form of labour, capital, or equipment) and either intermediate outputs (numbers treated, waiting time, etc) or final health outcomes (lives saved, life years gained, quality adjusted life years (QALYs)). Although many evaluations use intermediate outputs as a measure of effectiveness, this can …