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Abstract This paper presents the results of the evaluation of paraffin control treatments applied in rod pumped wells in La Concepcion oilfield, located at the western of Venezuela and operated by Petrowayuu, which is a mature field with paraffin deposition problems. Before the study, the only treatment applied on the wells to control paraffin deposition was hot watering. Because the average production rate of the wells was 30 BFPD, the application of high volume treatments, as hot watering, implied production deferral due to their low productivity index (around 0.09 BFPD/psi). Paraffin dispersant cold batch was used as an alternative treatment. To assess the effectiveness of the paraffin control treatments and their optimal application frequencies, it was necessary to use scale coupons observation, flowline pressure monitoring, and dynamometer cards analysis. It was found that paraffin dispersant cold batch treatment resulted to be the most cost-effective way to control the problem in all of the wells evaluated and the optimal batch treatment frequency was determined for each well. Moreover, most of the wells had been treated in a very low frequency. Besides this, it was demonstrated that circulation of high volume of hot water generated production deferral. This enabled Petrowayuu to increase its earnings in approximately 500,000 U.S. $/yr, compared with hot watering costs, mainly because of production deferral reduction. Introduction Over the years, paraffin deposition has been a constant problem in the rod pumped wells of La Concepcion field. This deposition has been observed during pulling jobs (Fig. 1) in which approximately 1.000 ft of tubing are plenty of solid paraffin. An analysis of the subsurface rod pump failure statistics, which included data from 2003 to 2005, revealed that paraffin deposition resulted to be the main cause of the failures (Fig. 2). To control the problem, Petrowayuu had tried several methods such as, steam injection, magnetic devices, bacteria injection, hot oiling, and lately hot watering. All of the methods applied had resulted to be unefficient or non cost-effective. As a result of this and based on the experience that A. Haudet had in Medanito, it was developed a methodology to determine the optimal paraffin control method and frequency for each well. This methodology combined the use of scale coupons observation, flowline pressure monitoring, and dynamometer cards analysis. Once the most cost-effective treatment was applied, production deferral due to hot water jobs was reduced to a minimum. Methods of Paraffin Control There are many literatures reporting methods of paraffin control[1,2], they can be divided into four categories: Mechanical, thermal, chemical, and combinations of those. Mechanical methods basically include scrapers. On the other hand, thermal methods include steam injection, bottomhole heaters, and circulation of hot oil or hot water. In hot watering, heated water is pumped down the tubing or casing when there is no packer. Chemical methods include solvents, wax crystal modifiers, and paraffin dispersants. Paraffin dispersants are surface-active agents that dissolve the paraffin deposited on the tubing wall. In cold batches, water provides the dispersing medium for the paraffin compounds while is carried out of the well. In some cases, one method is not enough to control the problem itself, so it is necessary to combine them. Methods of Paraffin Deposition Assessment The methods of paraffin deposition assessment used in this study were dynamometer cards analysis, scale coupons observation, and flowline pressure monitoring. Analysis of dynamometer card is the main diagnostic tool for rod pumped wells. Paraffin can cause an increase of the load on the polished rod, so a treatment that removes this deposition will cause a decrease on load. Scale coupons are metal pieces with small holes that promote scale deposition; they are commonly used in water systems, and are inserted in the flow stream to simulate what happens in the inner walls of the lines. By observing an exposed coupon, valuable information can be provided regarding the effectiveness of an applied treatment (Fig. 3).
- North America > United States (0.68)
- South America > Venezuela > Lake Maracaibo (0.54)
Abstract The standard use of the centrifuge is to determine capillary pressure in plugs. What is proposed in this work is to extend its application making it possible to determine the pore-throat size distribution in plugs in addition to the capillary pressure indicated above. To this end we start with a plug properly cleaned and saturated with the corresponding brine. The plug is then placed in the centrifuge and the collected data consists of the total evacuated brine volume VT(n) as a function of the centrifuge rotation speed n. A simple model, consisting of capillary tubes running from one end of the plug to the other, is proposed to describe the complex system network of pores and the corresponding interconnecting pore-throats. The corresponding theory, based on treating the capillary pressure as that due to the water-air interphase, is worked out in such a way as to link the capillary size distribution to VT(n) vs. n. The mathematical procedures turn out to be straightforward and the solution is unique. This original analysis of the centrifuge data was successfully applied to a large number of plugs. As an example the corresponding data and analyses are fully given and described. In a companion paper these results are compared with those obtained by MICP (Mercury Injection Core Porosimetry), and the agreement found may be considered as excellent. There is a practical limitation of the method proposed in this work. The capillary pressures that can be reached with the centrifuge are not as high as those that can be reached by MICP. This limitation manifests itself in the fact that pore-throat sizes below 1 mm are poorly detected or not detected at all. However, for pore-throat sizes above that value the agreement is excellent. The main result obtained in this work is that it is shown that similar information to that produced in a MICP run with two main advantages (1) the centrifuge is a non-destructive experiment, and (2) is a non-contaminating experiment. Introduction Porosity of formation rocks is one of the most relevant petrophysical characteristic parameters. Porosity is made up of pores and pore-throats and their sizes span wide range of values from about 10–2 mm up to 103 mm, and their sizes distribution functions are very important for a proper evaluation and management of an oil field. There are not many experimental techniques to determine these distribution functions in bulk formation rocks (plugs). They are NMR (Nuclear Magnetic Resonance) and MICP (Mercury Injection (or Intrusion) Core Porosimetry). No one of them provides the information we are looking for. Also, in real formation the pores and the pore-throat network interconnecting them is so complex that it is not always possible to clearly discriminate among pores and pore-throats. NMR measurements provide an information called the T2-distribution function, which rigorously speaking correspond to the addition of both the pore and the pore-throat sizes distribution functions, and it is not possible to separate them out. One of the most appreciated advantages of NMR is that it is a non-destructive technique. On the other hand, MICP provides a good description of the pore-throats sizes present in the plug weighed by the fraction of the porosity corresponding to the pores interconnected by that given pore-throat size. Additionally, and unfortunately, MICP experiments are destructive and contaminating. Thus, neither NMR nor MICP are able to provide the pore and the pore-throat size distributions. In this work we propose to carry on a new experiment, the WRC (Water Removal by Centrifuge), using the centrifuge whose results resemble those obtained by MICP but with the main difference that is a non-destructive and non-contaminating one. In the following sections the basic theory is developed, the equipment used (the centrifuge) is described, the results obtained in a standard plug are presented, and the conclusion is that a new method to determine the pore-throat sizes which closely resembles the results obtained by MICP. Limitations and advantages are described.
- South America > Argentina (0.28)
- North America > United States (0.28)
Abstract In order to improve the seismic imaging and delineation of a reservoir, an OVSP was run in an exploratory well; Neuquén Basin; Argentina. A second purpose of this acquisition was to accurately locate an Intermediate Casing above the main target. Acoustic Impedance Inversion of the corresponding Zero Offset VSP plus the image interpretation generated from the OVSP data helped to define the position of a sill, which was one of the objectives in this project. The thick (hundreds of meters) and extensive Auca Mahuida volcanic complex which covers most of the region, considerably reduces the signal to noise ratio of the seismic data; strongly attenuating the high frequencies of the data due to wavefields dispersion, hampering their separation at the processing stage. This effect is stronger in surface seismic than in borehole seismic, due to greater offset and two-way traveltime, so that VSP is used as a tool in this environment. Therefore, Q factor estimation (and consequently Q inverse filtering application) computed directly from Zero offset VSP, is a very valuable technique which allowed us to recover high frequencies in the field area improving vertical seismic resolution and helped to define the reservoir with greater accuracy. An acoustic impedance inversion of the VSP trace was later obtained, and its interpretation was very useful to predict impedance variations, related to lithology and formation changes in the deeper portion of the stratigraphic column. This was the first deep exploratory well (4750 meters) in this part of the basin, so the implemented technique led to define deep formation tops. The acquisition was performed by Schlumberger using the multilevel 3C high-fidelity downhole tool, Versatile Seismic Imager (VSI). It was used two vibrators simultaneously in flipflop configuration for both source positions in order to reduce the operational time. Introduction In this paper we describe the objectives, methodology and results of a Borehole Seismic Job performed in an exploratory well, YPF.Nq.LoAm.x-1 (Loma Amarilla), La Banda Block, Neuquén Basin. This block is entirely covered by volcanics from Auca Mahuida Igneous Complex. At the well location it was estimated 100 to 150 meters of surface volcanics. So that, in this area, the 3D seismic volume acquired in 2003, presents a poor to fair signal to noise ratio; and low frequency content (Fmax ˜40 Hz). Fig. 1. The main targets of this project were two igneous bodies, intruded as sills; the deeper one in Cuyo Gr.; and the shallower in the Vaca Muerta shales. Fig 1: Visualization of Borehole, 3D Seismic, Satellite Image and Topography. The presence of basalts in the area is affecting the recovery of high frequencies reflected in the subsurface; for this reason, surface seismic is very poor in terms of resolution and it is expected that the image obtained through the OVSP helps in the interpretation of the area. The job was planned in 2 phases, intending to acquire a ZVSP from surface to 2480m in the first phase, for the second phase a ZVSP from 2480m to 3580m and also an OVSP. The first VSP data was used to calibrate the model and determine the best position for the OVSP (based on survey design). In the second phase, Q factor was estimated using ZVSP, a migrated image was obtained from the OVSP, and an Acoustic Impedance Inversion was performed using the ZVSP. Finally, all the information was merged to obtain a complete time-depth relationship, corridor stack and Q factor estimation.
- Geology > Geological Subdiscipline (1.00)
- Geology > Rock Type > Igneous Rock > Basalt (0.62)
Abstract Ultrasound or high frequency (20 kHz-100kHz) pressure wave has been used in diagnose and treatments in different areas, such as: medicine, dentistry, civil engineering, and many other industrial applications. In Oil industry there are applications such as pipeline inspections, fluid velocity measurements, etc, but to the present its application in formation stimulation has been incipient, and only few lab and field test experiences have been reported. Stimulation with ultrasound is not a common operation offered by oil service companies. In order to visualize the real potential of ultrasound in oil well stimulation, it is necessary to understand the wave phenomenon, its properties, the parameters that define its behavior, and its interaction with the propagation media. This basic knowledge together with the understanding of the different formation damage mechanisms are the keys to comprehend the real potential and application window of the ultrasound in oil well stimulation. The present paper presents the theoretical basis of ultrasound and wave phenomena that must be considered when thinking about stimulation with ultrasound. Finally some suggestions about the application window of this technology are given. Introduction Ultrasound has been applied in many areas such as: diagnosis, quality control, inspections, cleaning, etc. Industrial cleaning is achieved flaking out the particles by mechanical action of the pressure waves (Fig 1). Usually the piece is submerged in fluids inside a container whose walls are fixed ultrasonic sources. Clearly, there is a great difference with an application for oil well stimulation, where the source is running inside the hole and the cleaning area is around the source. Each application has a particular frequency and power associated according to the sample dimensions and the purpose: for example, the power and frequency used for control echography in pregnant mothers are different than the used in muscular therapeutic treatments. In the first case is enough to detect an echo with high resolution (higher frequencies). In the second case it is required to transfer energy to the tissue, but high resolution is not required (lower frequencies). It is clear that the purpose and the propagation media affect the ultrasound parameters, highlighting the importance to understand which are the damage mechanisms where ultrasound could be applied and viceversa. Figure 1. Piece before and after Industrial ultrasound cleaning. The advantage of applying ultrasound comparing with conventional stimulation is that no invasion or external fluids are required, avoiding fluid/rock interaction analysis, the placement and the associated equipment and risky operation of handling high pressures at the wellhead. Additionally, ultrasound would allow under balance treatments without shut-in the well. Ultrasound cleaning is not a common tool offered by service companies in the field. Just some field tests in China and Russia have been reported with more qualitative than quantitative information making these tests not conclusive. Recent references about lab experiences and tool prototypes suggest the potential of this technology. However, ultrasonic stimulation has low understanding of the phenomena that are taking place in the porous media, how the waves are interacting with the matrix and the trapped particles. The parameters for suitable cleaning with ultrasonic treatment are not well defined and how these parameters change while the wave is propagating in the porous media is not clear either.
- North America > United States (1.00)
- Asia (0.69)