Reduced production is often caused by local impairment of the formation permeability due to the interaction of the reservoir with drilling and completion fluids. The problem may be further compounded by impairment caused by fines migration during production. High frequency sonic and ultrasonic waves have been used in many industrial applications to remove contaminants like dirt, oil, and grease from parts immersed in fluids. An obvious extension of this application is the removal of wellbore impairment by exposing it to high frequency acoustic waves. The influence of high frequency waves is limited to the near wellbore environment due to high attenuation. Dedicated experiments under realistic downhole conditions have been carried out in both linear as well as radial configurations. We have examined the acoustic power needed to remove near wellbore formation damage due to fines and particles plugging and drilling induced damage. Specific issues related to well completion and envelope of acoustic stimulation are presented. The laboratory results have led to the design and construction of a slim, high power and high frequency (above 10 kHz) downhole acoustic tool for field deployment. This paper outlines the concept and presents key experimental results to support the claim. Key features of a prototype downhole tool are described. Introduction Acoustic waves are traditionally used in the oil industry for exploration and appraisal during seismic and logging surveys. Recently, with the advent of 4D technology, repeated seismic surveys are carried out to monitor the production behavior of a field. Surprisingly, acoustic waves can also be used for production enhancement. The two main potential applications are near wellbore cleaning and enhanced oil recovery. This paper highlights the key development and understanding in the wellbore-cleaning area, specifically, high frequency acoustic stimulation. Formation damage can arise from many well activities during drilling, completion and production. The associated damage mechanisms are numerous. One of the most pervasive mechanisms is the plugging of pores by solid particles. This may be caused by external sources such as drilling mud and drilled solid invasion, or may originate in the porous medium itself, for example when in-situ clay fines are mobilized during production. It is not always possible to prevent formation damage completely, and well stimulation techniques to remove or mitigate the impact of formation damage have been used in the industry since more than half a century ago. Although conventional well stimulation techniques - both matrix and fracturing stimulation - have been applied very successful, they do suffer from some severe limitations. Acoustic cleaning presents a promising new well stimulation technology in the combat against formation damage. It complements the existing stimulation technologies and enlarges the range of options available for cost effective well stimulation. It uses high frequency sound waves to shake loose damaging particles and facilitate their removal by flowing the well. The following discussion substantially enhances and complements that given by Wong et al1. We first outline the motivations and potential applications of acoustic stimulation. Then, experimental data are presented to illustrate cleaning efficiency of acoustic stimulation. Finally, key issues surrounding the design and testing of a prototype downhole tool are expounded. Acoustic stimulation field trials are being planned but details are left to future publications. Conventional Well Stimulation Both matrix stimulation and hydraulic fracture treatments involve the pumping of specialized fluids. Therefore, these techniques are ‘invasive’ and two critical issues immediately become paramount:compatibility between injected fluid and in-situ rock/fluid, tubing and even surface equipment, andfluid placement, diversion and penetration into the rock.
During the Advent-99 experiment, which took place in the Sicily Strait in May, 1999, multitone (in the band 200–1500 Hz) narrow-band signals were transmitted from a bottom-mounted tower and received on a 64 phone line array (VLA) covering the water column; the water depth was 80 m. Data at a source–receiver range of 10 km will be presented and modeled using an internal wave model. A CTD chain containing 48 CTDs on a vertical string was towed continuously during the acoustic experiments between the source and VLA, yielding a time-evolving sound speed profile between the source and receiver. From that the average buoyancy frequency and sound speed profile were determined as a function of range. Internal-wave-mode depth functions were calculated using the measured buoyancy profiles. Internal-waves-mode amplitudes were determined from the eigenvalues of the sound speed covariance matrix for the lowest 5 modes. Internal-wave-frequency spectrum has the typical 2-power dependence as in the Garrett–Munk model. The modeled results of mean transmission loss and amplitude fluctuations with and without internal waves will be presented and compared with data. [Work supported by the Office of Naval Research and SACLANTCEN.]
The vertical directionality of acoustic ambient noise has been a subject of much interest in the past. It is a well-defined physical quantity that can be measured experimentally with a vertical array. It possesses certain deterministic features that can be modeled theoretically with environmental acoustic and source data. Ambient noise in shallow waters, including its vertical directionality, is not very well known and is also difficult to model/predict. This is because the acoustic environment varies with time and is location dependent. Thus arises the question, how does the vertical directionality of the ambient noise depend on the acoustic environments (found in typical coastal waters)? Due to the shallow water depth, it is noted that sound (noise) propagation can be significantly influenced by the bottom. The degree of bottom interaction will depend on the sound-speed profile in the water column: whether it is downward refractive or not. Bottom attenuation will in turn determine how far the sound will propagate in the water column. Using a modal representation, a closed-form expression is obtained which can be used to interpret and predict the distant noise vertical directionality as a function of the environmental acoustic parameters. The nearby (overhead) noise is separately modeled and is found less sensitive to environmental changes as the propagation distance is short. As the deterministic features of the noise vertical directionality is controlled by the sound propagation in the channel, it could be used as an acoustic indicator of the acoustic environment in the area. Time variations of the noise directionality will also be discussed.
Source localization is a challenging problem in a time-varying random shallow-water environment in the presence of internal waves. The short correlation time of the acoustic field (a couple of minutes) makes it difficult to adjust the replica field in response to the environmental changes. Also, mode couplings induced by the internal waves are random and not predictable. In this paper, the effect of mode coupling on source localization in the presence of Garrett–Munk and solitary internal waves is investigated. It is found that mode coupling affects practically all modes in shallow water. Random-mode coupling reduces the matched-field correlation. To improve source localization, a broadband matched-beam processing algorithm is proposed to suppress the noncoherent coupled-mode contributions. It is shown that this technique significantly improves the localization performance over conventional matched-field processing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.