Roller-Bit Penetration Rate Response as a Function of Rock Properties and Well Depth
- B.H. Walker (Terra Tek Inc.) | A.D. Black (Terra Tek Inc.) | W.P. Klauber (Terra Tek Inc.) | T. Little (Terra Tek Inc.) | M. Khodaverdian (Terra Tek Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 5-8 October, New Orleans, Louisiana
- Publication Date
- Document Type
- Conference Paper
- 1986. Society of Petroleum Engineers
- 1.6 Drilling Operations, 1.2.3 Rock properties, 5.3.4 Integration of geomechanics in models, 1.14 Casing and Cementing, 1.5 Drill Bits, 5.8.2 Shale Gas
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A rate of penetration (ROP) prediction equation for an insert roller cone bit is determined from laboratory drilling tests as a function of bit weight, well depth and laboratory measured rock properties. A complete description of each of the properties. A complete description of each of the seven rock types used in the study is presented. A comparison of ROP at different flow rates for each rock shows minimal hydraulic cleaning problems at the base hydraulic energy levels chosen. problems at the base hydraulic energy levels chosen. The predictive equation will be valuable in predicting drilling rate and understanding how the predicting drilling rate and understanding how the rock properties affect it.
A predictive equation for oil field, insert-type roller bit rate of penetration (ROP) based on rock properties and well depth has never been established properties and well depth has never been established experimentally. Considerable work has been done to correlate ROP with bit weight and rotary speed, flow volume and a "formation constant". The "formation constant" is arrived at from information available from previously drilled
sections of offset wells by calculating it from the known ROP, using the inverse of an ROP prediction equation. If ROP can be determined as a prediction equation. If ROP can be determined as a function of measureable rock properties in the laboratory under in-situ stress conditions simulating the downhole environment, then a general ROP prediction method will be possible. It also gives insight into which rock properties affect ROP.
A correlation between selected rock properties and well depth with ROP for a tungsten carbide insert, IADC code 5-3-7, roller cone bit is determined. Ten different rock properties for each of the seven rock types were used in the correlation along with bit weight and well depth. The bit was tested under fully-simulated drilling conditions at depths simulating 1,200, 4,400 and 8,800 feet [360,1320 and 2640 m]. Tests were run with 10.0 lb/gal [1198 kg/m**3] water-base mud with a range of bit weights typically used in the field with this bit type. Rotary speed was held constant. Flow rate was varied to determine if bit cleaning was affecting performance at the hydraulic energy levels used in the study.
Seven different low permeability rocks, with a wide range of rock properties, were used. The low permeability rocks were selected in this basic permeability rocks were selected in this basic study to eliminate the complexities added by the pore pressure changing between pores in the rock pore pressure changing between pores in the rock during the drilling test. Some of the rock properties considered included: mineralogy, properties considered included: mineralogy, unconfined compressive strength, average grain size, sonic velocity, in-situ compressive strength, Young's modulus, porosity, etc. An empirical equation of bit ROP as a function of bit weight, well depth and these basic rock properties is given. Since the basic laboratory rock properties are not always available, an alternative empirical equation is also determined which relates ROP to bit weight and well depth and to a simple rock indentation test. Both equations give reasonably good estimates of what the ROP will be for a given rock type. The variation in performance as a function of rock properties is shown and discussed.
The effects of confining pressures on rock properties are well known. As the confining pressure properties are well known. As the confining pressure is increased both the strength and ductility of rock increases.
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