Investigation of Various ROP Models and Optimization of Drilling Parameters for PDC and Roller-cone Bits in Shadegan Oil Field
- Mahmood Bataee | Mohammadreza Kamyab (Petroleum U. of Tech Iran) | Rahman Ashena (Petroleum U. of Tech Iran)
- Document ID
- Society of Petroleum Engineers
- International Oil and Gas Conference and Exhibition in China, 8-10 June, Beijing, China
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
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According to the field data, there are several methods to reduce the drilling cost of future wells. One of these methods is the optimization of drilling parameters to obtain the maximum rate of penetration (ROP) in each bit run. Many parameters affect ROP like hole cleaning (including drillstring rotation speed (N), weight on bit (WOB), floundering phenomena, mud rheology), tooth wear, formation hardness (including depth and kind of formation), differential pressure (including mud weight (MW)), etc. Considering the geology and rock mechanical parameters, each part of well has different recommended parameters from the other parts. To optimize the drilling parameters, it is required that an appropriate ROP model to be selected until acceptable results are obtained. In literature, there are various applicable models to predict the ROP such as Bourgoyne and Young model, Bingham model and modified Warren model. It is desired to calculate and predict the proper model of ROP for roller-cone and PDC bits in each well by using the mentioned models and then verify the validity of each model by comparing with field data. Analyzing the drilling parameters by computer optimizationyields recommended range of parameters for each bit. The applications of present study are predicting the proper penetration rate, optimizing the drilling parameters, estimating the drilling time of well and eventually reducing the drilling cost for future wells.
The rate of penetration achieved with the bit has a direct and obvious effect on the cost per foot drilled. There are some variables, which affect the rate of penetration. Lots of experimental work has been done to study the effect of these variables on drilling rate. These factors that affect the rate of penetration are: Bit type, weight on bit (WOB), rotary speed (N), drilling fluid properties, bit hydraulics and formation properties.
Bit type is chosen in bit design method by sonic log of the offset wells. Mud weight and optimum hydraulics is also planned from nearby well. Formation properties could be considered constant in each formation. So, we can optimize WOB and N in the field to obtain the maximum ROP.
The relationship between ROP and N is shown in Figure 1. It is noted from this figure that the ROP is directly proportional to WOB till a critical point. The normal drilling trend ends in point c in the figure. Increases in rotary speed will also enhance ROP till hole cleaning problems occur. In soft formations, ROP usually increases with increasing N, but in hard formations it is a reverse relation. This is the primary reason that high rotary speeds (about 150-250) are usually used in soft formation and low rotary speeds (about 40-75) are used in hard formations.
Field history itself can be a good clue to choose some of the important parameters to improve penetration rate, like bit type, weight on bit, etc. the approach is to separate field into some sections due to geological similatrity; then analyze for each hole separately by their performance.
Before reviewing ROP models, we should do some assumptions to achieve an appropriate formula:
• The study done in three different hole sizes 13 3/8'', 9 5/8'' and 7'' so bit diameter (db) is a constant value.
• The mud properties, pressure differential, rock properties and selected bit (according to IADC code) are related to depth in each hole size.
• Threshold bit weight is neglected according to lack of drill off test in the field.
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