Review of Cuttings Transport in Directional Well Drilling: Systematic Approach

Hole cleaning during directional well drilling is a major concern in the oil patch and must be monitored and properly controlled during the entire drilling operation. Inadequate drilled cuttings removal can cause many costly problems such as mechanical pipe sticking, excessive torque and drag, difficulties in casing/cementing and in logging. Low fluid annular velocity, lack of drill pipe rotation and the wrong mud properties are primary factors in the inadequacy of effective hole cleaning. This paper presents a thorough review on previous hole cleaning studies and discusses an approach that uses physical-systematic methodology that is more suited for monitoring and controlling hole cleaning problems. The approach is based on relating output and internal state vectors to input vectors. The concept basis is to classify the drilling parameters into inputs, internal states and outputs, check the observability (condition monitoring) and controllability of the hole cleaning as an internal state during drilling. Previous studies on drilled cutting transport can be grouped in four categories: Sensitivity analysis –internal states changes vs. input changesModeling – physical relations of inputs and internal stateMonitoring – using real time measured data to estimate the internal stateControl – change inputs until achieving the desired internal state