A.L. Podio

Nonlinear viscoelastic behavior of sedimentary rocks, Part I: Effect of frequency and strain amplitude

Sedimentary rocks display nonlinear elastic behavior. This nonlinearity is a strong function of frequency, strain amplitude, and the properties of the saturating fluid. Experimental observations and potential mechanisms that cause these nonlinearities are presented in this and a companion paper. Young’s moduli and Poisson’s ratios obtained from ultrasonic laboratory measurements (50 kHz, 100 kHz, 180kHz and 1 MHz), low‐frequency measurements (1–2000 Hz) and static measurements (0.001–0.05 Hz) show significant differences under identical stress conditions. A comparison of the laboratory‐measured quantities with log‐derived moduli measured at 20 kHz indicates that Eultrasonic>Elog>Elowfreq>Estatic. This shows clearly that a wide variety of sandstones demonstrate frequency‐dependent elastic behavior (viscoelastic behavior) over a range of frequencies. Differences between static (low‐frequency, high‐strain amplitude) velocities and ultrasonic velocities can be explained partially by differences in frequency a...

An experimental investigation of factors influencing compressional‐ and shear‐wave velocities and attenuations in tight gas sandstones

Results are presented for compressional and shear velocities and attenuations in fully brine‐saturated tight gas cores with porosities from 3 to 11.9 percent and clay contents from 1 to 38 percent. The influence of porosity, clay content, frequency, and stress on velocities and attenuations were examined using the amplitude spectra of P‐ and S‐waves in the frequency domain. Attenuations of samples were obtained using the spectral ratio method. For a few selected samples the attenuations were also measured using the length correlation method and these results were compared with the spectral ratio results. In tight gas sandstones, the attenuations obtained were 2 to 5 times greater than the attenuation obtained for Berea sandstone. In general, the presence of clay softens the rock grain contacts causing smaller values of compressional (VP) and shear (VS) velocities as the clay content increases. However, the VP/VS ratio was found to increase with clay content. Compressional‐and shear‐wave amplitude spectra ...

Trends Extracted From 800 Gulf Coast Blowouts During 1960-1996

The cost of blowouts and the loss of life incurred from blowouts warrant the study of past occurrences in order to reduce number of future blowouts. Even though we continuously learn more about how to handle an unstable well, it seems that the problems of detection, handling kicks and loosing control do not change much with time in the real world out on the rig, The small changes and improvements that do occur are first of all seen thorough statistical data. A new data base resently compiled will soon contain extensive data on more than 800 blowouts from the Gulf Coast area and adjoining states duting the period 1960 through 1996. At the moment the compiling work has not been completed. However, at the 1998 [ADC/SPE Drilling Conference an updated version of this paper will be available. Five agencies contributed blowout report information. The State Oil and Gas Boards/Conservation Office of Alabama, Mississippi and Louisiana, The Railroad Commission of Texas and the Mineral Management Service (MMS) of the Dept, of Interior. At the moment the Texas blowouts makeup approximately 50V0of the blowouts in the data base but range below the average blowout frequency of 0.15 blowouts pr. 100 well-ft. drilled. The three major operations in progress when blowouts occurred were exploratory drilling, workover and development drilling. Most frequently blowouts occurred during the activity of actual drilling, tripping out and circulating/killing. The analysis indicated also that the major causes were related to swabbing, drilling into a high pressure zone or formation break down while the secondary barrier after a kick has occurred which most often failed were either failure to close BOP, failure to stab string valve or BOP failed after closure, Introduction Control of the formation pressure is an important concerr both in the planning phase and during execution of the drilling operations. Improper procedures with respect to detection and handling of kicks may result in loss of control. The cost of blowouts and the loss of lives incurred from blowouts warrent the study of past occurrences in order tc reduce the possibilities of titure blowouts. We are hoping to see that operating experience in general and experience through required blowout schools especially is slowly paying off. Technology changes may however override these effects in both directions. Examples 01 technology changes are diverterless drilling combined with drilling in deeper water and pushing the surface casing deepel and deeper/fewer casing strings, thus causing a changing risk and not necessarily accompanied by a corresponding reassessment of the kick detection/killing procedures. Since the shallow gas hazard and consequences are above normal, large improvements have been noted the last decade or twc with respect to shallow seismic and kick detection systems for floaters. Method of Analysis On basis of data from five data sources ●State Oil and Gas Board of Alabama ●Louisiana OffIce of Conservation ●Mississippi State Oil and Gas Board ●Texas Railroad Commission (RRC) ●Minerals Management Service (MMS) (Outer Continental Shelf)

Killing Methods and Consequences of 1120 Gulf Coast Blowouts During 1960-1996

This paper focuses on what happened after wells are out of control by analyzing statistically a database that contains about 1120 blowout events from the Gulf Coast and adjoining states covering the period 1960-1996. The trends are extracted, including blowing fluid type, mode of control, duration of blowout, pollution, fire and explosion, and fatalities. Detailed differences between Outer Continental shelf (OCS) and Texas are given. A report form of blowout events is recommended in order to improve the data quality and standardize reporting. Introduction Drilling engineers and fire-fighting specialists never stop investigating blowouts because of the cost of blowouts, the loss of life and pollution incurred from blowouts. One logical counter measure is to analyze statistical data, revealed the weakest points and attack them. Blowout databases have been developed to extract trends from blowout events since 1990. Kato and Adams set up a database containing 905 blowouts and analyzed the trends . Their data were mainly collected from Alberta, Canada, Texas, USA, and the Gulf of Mexico. They investigated statistically the pollution possibilities from blowouts, causes, duration and kill methods. Danenberger 3 put special attention to Outer Continental Shelf (OCS) drilling Blowouts by 87 events from 1971-1991. He found that most of blowouts were attributable to shallow gas influx, and were of short duration. Hughes, Podio and Sepehrnoori 4 initially developed a database in 1990, which is updated regularly. The data are mainly from Texas, OCS as well as Louisiana. This database contains almost all blowouts in Texas and OCS. Partial trends were extracted from the updated database in a previous paper, including blowout depth, blowout causes, operation in progress and etc. Present paper is a follow up of a recent paper, which focuses on what happened after the blowouts were underway. The updated database contains 1120 blowout events from the period between 1960 and 1996, geographically distributed as follows: 826 in Texas, and 187 in the Outer Continental Shelf (OCS). The remaining 110 from Louisiana, Mississippi and Alabama are incomplete and not included in this paper. Five agencies contributed the blowout data: State Oil and Gas Board of Alabama, Louisiana Office of Concervation, Mississippi State Oil and Gas Board, Texas Railroad Commission (RRC) and Minerals Management Service (MMS.). This article analyses the following aspects: blowing fluid type, mode of control, blowout duration, pollution, fire and explosion, and fatalities. No systematic method to report blowout existed before 1973. Although it has been mandatory to report the events in United States since 1973, a more detailed and standard reporting is needed, and a blowout report form is recommended. Blowing Fluid Type The blowing fluids are categorized into 11 groups as shown in Table 1. Shallow gas is defined as gas which comes from depths shallower than 2000 ft or for wells with the last casing set at only 200 ft. There are 22 wells (2.7%) and 6 wells (3.2%) where fluid type are missing in Texas and OCS respectively. Pure gas blowouts account for 76.4% in OCS, including 57.7% gas and 18.7% shallow gas. Flow of liquids occur in 10.6 % blowouts, and 9.6% events compound to a mixture of Gas and liquids. In Texas, the blowout occurrences caused by pure gas (as well as shallow gas), liquids, and mixtures of gas and liquids are 50.3%, 8% and 39%, respectively. Obviously, gas is by far the most dangerous kick medium. It is noted that 89.3% and 86% of the blowouts contain gas in some forms in Texas and OCS. Figure 1 shows the clear difference in fluid types between OCS and Texas. It is apparent that there are more dangerous gas blowouts in OCS than in Texas. Especially in OCS exist 35 (18.7%) shallow gas events, but only 2 wells (0.2%) in Texas. It is only in OCS that oil blowouts (9 wells, 4.8%) and condensate blowouts (7 wells, 3.7%) were reported. In Texas occurrences are characterized by 198 wells (24%) blowing SPE 53974 Killing Methods and Consequences of 1120 Gulf Coast Blowouts During 1960-1996 Skalle, P./NTNU, Trondheim, Jinjun H./Southwest Petroleum Institute, Nanchong, Podio, A.L./UT, Austin 2 SKALLE, P., JINJUN, H., PODIO, A.L. SPE 53974 mixtures of gas and water, as well as 3.6% mud. This difference is real, but partly caused by an imprecise reporting form. Mode of Control Blowout control methods are divided into 8 categories: Collapse of open hole wellbore (Bridging), Closing the blowout preventer (BOP), Pumping Cement slurry (Cement), Capping, Depletion of small reservoirs, Install equipment, Pumping Mud, and Drilling Relief wells. Figure 2 and 3 give the modes of control in OCS and Texas respectively. Figure 4 compares the two areas. In OCS, bridging is the most common control of blowouts with 39.6%. Killing with weighted mud ranks second with 19%. In Texas, mud is the favorite method, accounting for 41% of total killing events, while bridging ranges second with 19%. 11% of Blowouts were killed by means of cement in both areas. Other modes of control such as BOP, depletion, install equipment and relief well, have almost same importance in OCS and Texas. Duration Blowout duration has a wide range from 0.0 to 10800 hours (about one and half years) according to the database. Figure 5 shows the proportion of blowouts vs duration. In OCS, 12% more occurrences (15%-3%) than in Texas ceased in less than one hour, which means that significantly more blowouts were controlled quicker in OCS. A little bit more blowouts lasted in 1-24 hours in Texas than in OCS. Only about 4% of blowouts continued blowing in more than one month in both areas. A cumulative percentage of blowouts vs duration is shown in Figure 6. Suffice it to say that the majority of the events were of short duration. 52.4 % and 44.9 % of the occurrences were controlled in one day or less in OCS and in Texas respectively, which demonstrated that duration in OCS was obviously shorter than in Texas. About 80% of blowouts stopped blowing in one week or less. In other words, only 20 % of blowouts continued blowing after one week. Some record about formations in which blowouts occurred. It is, however, only in Texas where enough records are available to extract trends statistically (see Table 2). In Texas, 189 blowout events took place reportedly in sand, 80 in lime and 11 in other rocks. The further studies are made in sand and lime. Table 3 and Figure 7 give the duration distribution in different rocks. Totally 51.1% of events ceased in less than 24 hours in sand, but only 43% in lime. Table 4 and 5 and Figure 8 show the relationship between duration and depth in two rocks. In sand, average duration of blowouts increases with depth. In shallow formation (< 1000 ft), the average duration is 58 hours. The average duration is 519.6 hours for each blowout when the depth is over 10000 ft. By comparison, the correlation in lime is not as clear as in sand. A partial reason may be the relative shortage of data in lime. In the column of < 1000 ft, there was only one record with a blowout of 300 hours. Blowouts happening in the depth from 1000-2500 ft lasted in average 19.5 hours. At the average depth of 4067 ft, the average blowing period was 114.9 hours. When the depth was over 10000 ft, the duration was 83 hours without counting the longest duration of 10800 hours. Pollution Blowout pollution is divided in 4 levels according to the spills: Enormous ( >10000 bbls), Large ( ≤10000 bbls), medial (≤1000 bbls) and Small ( ≤100 bbls). Statistics are shown in Table 6. Pollution Rate is defined as number of pollution cases in 100 blowouts. It is clearly shown that 17.6% pollution rate is highest in OCS, while only 7.5% in Texas. As regard to the pollution size, most cases (24 of 33 in OCS, 44 of 62 in Texas, and 9 of 14 in Louisiana) are among the small size. Only in OCS we found cases (2) of enormous size in which spills are over 10000 bbls. It is concluded that blowouts in OCS have a higher risk of polluting the environment than in Texas. Besides oil, hydrogen sulfide (H 2S) is dangerous as an air pollutant. So far, there have been only 9 cases of blowouts in Texas that contained reportedly H 2S. The concentration of H2S ranged from 300 PPM to 12,000 PPM. The data are not enough to obtain trends. More attention should be paid to H2S pollution. According to data available, pollution rates are low and pollution sizes are small in all three investigated areas. The same conclusion as Kato 1 can be reached that a low probability exists for a blowout resulting in pollution. Fire and Explosion In some cases, blowout may cause fire and explosions, especially in gas blowouts. Table 7 gives the number of blowouts with fire or explosion in 3 areas. In the last column is the term, Fire Rate, which is defined as number of fire and explosion in each 100 blowouts (usually explosion incurs fire). Fire rate in OCS was 6.95%, which is twice as high as in Texas or in Louisiana. The main reason may be much higher percentage of gas (including shallow gas) blowouts as mentioned in Table 1. As the fire is dangerous to personnel and equipment, it is predicted that blowouts in OCS is much easier to cause loss of life than in Texas and in Louisiana, which has been demonstrated by the past casualties shown in Table 8. Fatalities Table 8 gives the data about deaths associated with blowout disasters. In OCS, 65 people died from 11 blowout events. It was gas blowouts that caused 60 fatalities. Oil rushing out from wellbore caused 4 persons to die. Therefore, gas blowing was extremely dangerous in OCS and contingency planning should be improved. In Texas, 14 casualties resulted from 9 blowouts. 4 people unfortunately died of blowing gas, while 10 deaths were from the mixture of gas and oil / gas and water. Number of fatalities in OCS was more than triple compared to Texas although the total number of blowouts SPE 53974 KILLING METHODS AND

Dual-Mode Ultrasonic Apparatus for Measuring Compressional and Shear Wave Velocities of Rock Samples

An ultrasonic apparatus and accUiate experimental techniques have been developed for measuring consecutively the bulk velocity of plane compressional and shear waves in samples of porous solid material. The apparatus was developed primarily to study the elastic behavior of rock samples recovered from well bores in the earth as deep as 7800 meters. Appropriate conditions of triaxial st(ess in the range 0-25 000 lbf/in2 (172 × 106 N/m2), fluid saturation, and temperature are imposed on the sample to simulate the surroundings of the parent rock in situ. In the apparatus, two electromechanical transducer cells operating in the frequency range 0.25-5 MHz are placed in direct contact with each end of the sample. Phase-coherent tone-burst pulses are used. The cells contain two sets of piezoelectric ceramic disks. One set generates and detects compressional waves, and the other set serves as the soUice and detector for shear waves, which form by mode conversion at an oil-aluminum interface. The mechanical ·design of the apparatus is based upon sound principles of geometrical acoustics. This method has substantial advantages over existing ones for testing rocks because it has greater accuracy and a shorter testing time. Transit times through nondispersive rocks can be measUied with a resolution of 10-8second. The time formerly required for making separate measurements of compressional and shear wave velocities has been reduced by one half. Velocities and elastic moduli are reported for aluminum, Solenhofen limestone, and Boise sandstone samples under stress.

Beam Pump Balancing Based On Motor Power Utilization

Recent application of a portable computer-based instantaneous power meter which is easily connected to a beam pump`s switch box, has made it possible to study in detail the effect of counterbalancing on electrical consumption and operating cost. This paper describes the measurement system as well as its application to determine the power usage per pump stroke and the gear reducer torque. A simple algorithm is presented for the determination of the counterweight adjustment required to modify the peak torque or the power use. The results of accurately monitored field tests for a variety of beam pumps and well depths are presented in detail. The measurements indicate that unit balancing based on instantaneous power, yields results similar to those obtained from torque derived from dynamometer measurements using a horseshoe type load transducer. The ease of installation of the power probes compared to installation of the dynamometer makes this the preferred method for most beam pumping systems powered by electrical motors.

Rotaflex Efficiency and Balancing

The RotaFlex pumping unit has a unique geometry that results in a constant torque arm (or torque factor) on most of the upstroke and downstroke. The geometry promotes high electrical efficiencies. Electrical efficiency can be measured by comparing the work required to raise the produced liquids from the net liquid level depth to the input electrical power. Also, electrical generation with the RotaFlex pumping unit is minimized compared to conventional beam pump units, which is favorable for high electrical efficiencies. RotaFlex balancing can be performed using electrical power measurements, and the amount of counterweight that must be added or removed from the counterweight box to balance the unit can be calculated directly by software using the power measurements and RotaFlex data. Power balancing does not require knowledge of the weight of the counterweight box and the auxiliary weights as is required with conventional mechanical balancing. An example of determining the electrical efficiency and of balancing a RotaFlex unit is given to further describe and explain the procedure for determining electrical efficiency and proper balance.

Pressure Transient Testing Using Surface Based Measurements

Proper reservoir management and production optimization require timely knowledge of formation pressure, permeability and well bore skin factor. To this effect, pressure transient tests using wireline conveyed pressure gauges are commonly run in flowing wells. The presence of artificial lift equipment complicates and often precludes the use of wireline conveyed devices so that conventional pressure transient tests are seldom performed in these wells, resulting in poor reservoir and production management. Since the 1980s, the industry has used programmable equipment for calculation of bottomhole pressure from surface pressure and acoustically measured liquid level data in pumping wells. Advances in electronics, computer software and transducer technology have vastly improved the data quality and the usability of this equipment to the point that routine determination of BHP using surface measurements is reliable, cost effective and provides real-time data with the quality necessary for pressure transient analysis. Seven field cases are presented to illustrate application of the acoustic pressure transient system in different wells and to illustrate best practices that results in high quality data. Introduction The present economic climate in the oil industry requires that maximum production efficiency be achieved with minimum engineering and technical manpower. Considering that the majority of US and Canada land oil wells are produced through artificial lift and the majority of these by means of beam pumping systems, there exists a need to easily monitor and analyze the performance of beam pumped and other artificially pumped wells. Flowing bottom hole pressure surveys, pressure buildup tests, pressure drawdown tests, and inflow performance analyses are the principal tools available to determine reservoir pressure, formation permeability, productivity index, pump efficiency, skin factor, as well as other indicators can be used in the optimization of producing well operations. These techniques are widely used in flowing wells and in some gas lift wells, where the pressure information is easily obtained from wirelineconveyed bottomhole pressure recorders. The presence of the sucker rods in beam pumped wells essentially precludes practical, routine, direct measurement of bottomhole pressure, thus eliminating the single most important parameter for well analysis. Permanent installations of surface indicating bottomhole pressure gages have not become cost effective or reliable over long periods of time. Wire line measurements PETROLEUM SOCIETY CANADIAN INSTITUTE OF MINING, METALLURGY & PETROLEUM

Plunger Lift Analysis, Troubleshooting and Optimization

A new portable monitoring system has taken the guesswork out of plunger lift analysis, troubleshooting and optimization. The plunger generates an acoustic pulse as it falls through each tubing collar recess when the well is shut-in. Each acoustic pulse travels through the gas in the tubing and is detected at the surface. The pulses are converted to an electrical signal by a microphone and pressure transducer. The signals are digitized, stored and processed in a computer to determine plunger position, plunger fall velocity, and plunger arrival at the liquid level in the tubing. The problem of not knowing the plunger location during the operation cycle has been overcome with this new technology by allowing the operator to see the plunger location at any time during the cycle. Having a detailed analysis of the operation of the well makes optimization of plunger lift production achievable with a minimum of effort and avoids the usual waste of time due to trial and error procedures. Example data collected from various plunger lifted wells are presented in this paper to show how to identify operational problems such as holes in the tubing, stuck plungers and plungers not getting to bottom

Decentralized Continuous-flow Gas Anchor

A novel gas separator design has been developed and successfully tested in several beam pumped wells which were subject to severe gas interference. This paper presents a detailed description of various designs to cover various ranges of fluid production for the most common sizes of completions (4-1/2 to 7 inch casing) and rates from 120 to 825 barrels of liquid per day. The new design is based on two innovations: decentralization of the gas separator in the casing, insures that a minimum amount of gas enters the separator; and the presence of two ports located on the narrow side of the annulus and placed a significant distance apart allow continuous flow of fluids into and out of the separator during both the upstroke and downstroke of the pump. These innovations have resulted in a gas separator efficiency much greater than that of conventional designs.