Rate of penetration

The rate at which the drill bit penetrates the formation gives qualitative information about the lithology being drilled. For example, in a hard shale the rate of penetration ROP) will be slower than in a porous sandstone. 

Considerable effort will be made to predict the onset of overpressures ahead of the drill bit. The most reliable indioations are gas readings, porosity - depth trends, rate of penetration and shale density measurements. 

Data transmission rate per foot is a function of both pulse frequency and rate of penetration. Sensors acquire and transmit data samples at fixed time intervals and therefore the sampling per foot is a function of rate of penetration. Current tools allow a real time sampling and transmission rate similar to wireline tools as long as the penetration rate does not exceed about 100 ft/h. If drilling progresses faster or if there are significant variations in penetration rate, resampling by depth as opposed to time intervals may be required. 

Fig. 2. Liquid flow-through capiUary (Washburn equation). Time rate of penetration = dl/dt = l/4[7/ 7] x [r/l] x cos0, where 7 = surface tension and 77 = viscosity. A, contact angle 9 between Hquid and capiUary waU B, penetrating Hquid C, partiaUy fiUed capiUary, r = radius, and I = length already filled.

Rate of penetration by height or volume Baiiiell cell... 

Rather high rates of penetration can be achieved since bit rotation speeds are high. 

For straight hole drilling the turbine motor with the highest possible torque and the lowest possible speed is of most use. Thus the turbine motor is selected such that the motor produces the maximum amount of power for the lowest possible circulation flowrate (i.e., lowest speed). The high power increases rate of penetration and the lower speed increases bit life particularly if roller rock bits are used. 

In MWD, the recording speed is the rate of penetration which rarely exceeds 120 to 150 ft/hr or 2 to 2.5 ft/min, two orders of magnitude less than the logging speed. Counters can be made shorter and time constant longer (up to 30 s or more). This results in a better accuracy and a better bed definition. Figure 4-269 shows an example of comparison between an MWD gamma ray log and the wireline log ran later. 

The data acquisition rate is generally set so that the sample spacing of the sonic log (the distance between two acquired data points) ranges from 6 in. to 1 ft based on the anticipated drilling rate of penetration (ROP). 

The time elapsed between drilling and recording the data at a given depth can be read in Table 4-131 for various rates of penetration. 

The weight transfer is also an important parameter that can decrease the rate of penetration. In deviated wells, up to 20,000 lb of weight and 25,000 ft-lb of torque can be lost to drag and friction. Figure 4-312 shows the improvement that can be caused by an 11-stand short trip and circulating a mud pill of 15 Ib/bbl of Barafiber. 

Bit Wear and Rock Type. Using downhole weight-on-bit and torque the roller cone bit wear can be estimated while drilling. The well site computer can be used to compute in real-time a dimensionless torque (T ) and a dimensionless rate of penetration (R ) using the following equation ... 

Is there a correlation between the shock number, surface weight-on-bit, rate of penetration, and RPM Explain. 

Example 24 Overpressure Detection with Rate of Penetration... 

The factors that influence the rate of penetration during a conventional rotary drilling process are numerous. In general these factors can be classified into five groups. 

T, = trip time (nonrotating time) in hr ROP = an average rate of penetration in ft/hr... 

Corrosion rates in normal industrial atmospheres measured as loss of weight over a period are extremely uniform among the various alloys. Table 4.19, last column, gives the corrosion rates (in g m d" ) for a number of alloys determined at Clifton Junction in recent years. The highest value recorded (0-4 g m d ) is equivalent to a rate of penetration of 0-076 mm/y, which is appreciably less than that of mild steel. 

Localised corrosion The various forms of localised corrosion are a greater source of concern to the plant designer (and operator) since it is usually difficult to predict an accurate rate of penetration, difficult to monitor, and consequently can be (especially in the case of stress-corrosion cracking) catastrophically rapid and dangerous. 

This test, which is frequently referred to as the Huey test, was first described and used by W. R. Huey in 1930, and since that time it has had wide application, particularly in the USA. The test consists of exposing the specimens (20-30 cmin fresh boiling 65% HNO3 (constant boiling mixture) for five successive periods of 48 h each under a reflux condenser. The specimens are cleaned and weighed after each period, and the corrosion rate (as a rate of penetration) is calculated for each period of test and for the average over the five periods corrosion rates are expressed as mm/y. The reason for the... 

The corrosion rate of a metal in terms of weight loss per unit area (g m" d ) or rate of penetration (mm y" ) can be calculated from Faraday s law if the current density is known. Conversely, the corrosion current density can be evaluated from the weight loss per unit area or from the rate of penetration. The following symbols and units have been adopted in deriving these relationships in which it is assumed that corrosion is uniform and the rate is linear ... 

To convert rate of penetration into weight loss per unit area per unit time (g m"... 

Corrosion Rate the rate at which a corrosion reaction proceeds. It may be expressed as a rate of penetration mm y", /xm s etc. (inches per year or ipy is still sometimes used), or as a rate of weight loss per unit area, for example g m" d", mg dm d (mdd) etc. It may also be expressed as the equivalent current density. 

By employing C14-labeled pyrethrum, it has been determined that at 35 °C. the rate of penetration of pyrethrum is more than twice that at 15°C. Cockroaches prostrate at 15 °C. can be returned to normal by transferring them to 35 °C., a process which can be repeated for several hours. Since cockroaches transferred from 35° to 15°C. became prostrate more rapidly than those held continuously at 15°C., the insecticide (or some metabolic toxin) was probably in the vicinity of its site of action at 35 °C. but was ineffective. 

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