Abstract: A turbine for use in a downhole drill string including an elongated casing defining an interior and a plurality of motor units in the interior. Each motor unit has a rotor and a stator. A torque transmission couplings connects each of the plurality of motor units to the drill string. The torque transmission couplings having flexible linkages. As a result, the power section has tight tolerances for the clearance at the tips of the rotors because the motor units are relatively stiff. The flexing normally obtained by bending the rotor shaft is accomplished and absorbed in the flexible linkages.

Abstract: A method of predicting a desired property, such as thickening time, of a cement slurry comprising measuring or determining other properties of a slurry composition and obtaining a predicted value of the desired property by applying values representative of the other properties to a model formed by determining the other properties for a series of cement compositions and correlating these with measured values of the desired property. In one embodiment the method comprises measuring and determining the other properties and inputting values corresponding to these properties to a neural network device configured to output a value representative of the desired property, the neural network device being a) configured to utilize each of said values as input values, b) provided with at least one hidden layer of at least one node, and c) trained with a dataset comprising series of values of said properties and a value corresponding to the desired property when measured for a slurry having the measured properties.