ECD - Effect of Cuttings
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It is well known when it comes to well planning that ECD management is an important topics. This is to avoid problems like kick, losses, fluid influx into the well and fracturing the formation among others. As more complex and deeper wells are encountered ECD management gets more excessive. While drilling a well cuttings will be generated. Dependent on different parameters like ROP, pumprate, rheology and viscosity the amount of cuttings created will fluctuate and make the cuttings concentration vary throughout the wellbore. The purpose of this diploma thesis is to see how the generated cuttings will effect the ECD. This is done by looking at different parameters which has an impact on the amount of cuttings generated and the cuttings concentration. Chapter 2 to Chapter 4 in this diploma thesis has are published knowledge on different parameters of ECD and cuttings. The primary emphasis of chapter two is ECD theory in general. Pore and fracture pressure, cuttings contained in the annulus and other factors influencing ECD are all presented in chapter two. Chapter 3 gives a short introduction of ECD problems regarding ER wells. The last theory chapter gives an overview of cuttings transport in both vertical and deviated wells. Chapter 5 is an overview of how the ECD model works. What assumptions has been taken into consideration, what calculations has been done, what input data has been used and how does the excel sheet work are questions that all will be answered in this part of the thesis. In Chapter 6 the results from the calculations done in this thesis are presented, and verified against field data. Results are eventually to be discussed in Chapter 7, and finally in Chapter 8 conclusions are drawn. From the steady state ECD model it has been found that ECD will increase for high ROPs, since a high amount of cuttings will be produced. A high pumprate will over time lower the ECD since cuttings will be transported faster out of the well. When the effective viscosity is kept high, the mud will have a greater ability to carry the cuttings out of the well, hence the ECD – Effect Of Cuttings IV ECD will be low. The mud density has probably not that large an effect of the cuttings concentration in the well, on the other hand is has a great impact on the ECD. If the ROP is really high, the effective viscosity and the pumprate should be kept high to get a sufficient hole cleaning. In some cases it is enough with either a high pumprate or a high viscous mud. If a low pumprate is combined with a low viscous mud it can be difficult to exceed the settlings velocity even for low ROPs.