Acoustic Logging Services
Missing important details about the surrounding rock can lead to decreased production and even wellbore collapse. Acoustic data processing helps to determine the borehole response to stress. Data computations for geomechanical parameters assist with hydraulic fracture designs, completion designs, seismic modeling and interpretation, and stress calculations in geological studies.
Acoustic measurements are critical in determining rock geomechanical properties, including anisotropy, pore pressure, wellbore stability, formation damage, sand strength, sand control, permeability attributes, natural faults and fractures, and hydraulic stimulation design.
Unconventional Reservoir Formation Evaluation Challenges Addressed With Deployment-Optimized Open Hole Logging Solutions
A. Hameed, M. Bacciarelli, and P.J. Williams, Weatherford
It is estimated that only one-third of the remaining worldwide oil and gas reserves are conventional, and the other remaining reserves are in unconventional reservoirs whose evaluation requires appropriate measurements delivered in a cost-effective way. In the case of shales and other tight reservoirs, the defining characteristics are low matrix porosity and low or ultralow permeability, which requires artificial stimulation to encourage production. The optimum stimulation strategy for a particular reservoir is strongly dependent on the distribution of organic material, on the mechanical and geometrical properties of the rock, and on the associated stress field. It is essential to quantify these to an appropriate level of certainty, and well logs are the primary source of such data. Until recently, the options for acquiring appropriate logs in high-angle and horizontal wells have been constrained by either the limited available sensors or the tool conveyance methods. However, the introduction of memory-capable, small-diameter, specialized tools and multiple innovative conveyance options has changed the cost-benefit balance for the better. This paper reviews the current status of openhole log measurements with full spectrum conveyance options and how they impact the evaluation of these challenging reservoirs.
Acoustic Dispersion From Phase Moveout in Array Sonic Data
S. Assous and P.A.S. Elkington, Weatherford
Borehole acoustic signals from dipole logging tools exhibit dispersion whose attributes depend on interactions between tool and borehole. The dispersion is a result of petrophysical and geomechanical properties of the rocks through which the wells are drilled. The starting point for their interpretation is the extraction of slowness-frequency curves for the modes of interest. This paper introduces a deterministic, nonparametric dispersion analysis method for the calculation of frequency-dependent slowness values. Conceptually simple, the method is based on phase moveout and transit time across the receiver array calculated at specific discrete frequencies, coupled with novel phase unwrapping and alias correction. The approach is entirely data-driven, requiring no prior assumptions about slowness ranges or the number of modes present, and results are free of the spurious events that complicate the extraction of dispersion curves from the popular weighted spectral semblance and extended Prony methods. This method is robust to noise and has superior slowness resolution relative to existing approaches, so it is better able to distinguish subtle variations between dispersion in the principal directions for anisotropic formations. Results have been validated using synthetic data, and field examples are used to demonstrate that dispersion curves are extractable over a wider frequency range relative to prior methods. The extended frequency range and good slowness resolution have the potential to improve estimates of shear slowness from the flexural mode low-frequency asymptote, and they increase confidence in the identification of stress-induced anisotropy from dispersion curve crossover.
Leveraging Slim Hole Logging Tools in the Economic Development of the Ghawar Fields
I. Ariwodo, A.R. Al-Belowi, and R.H. Bin Nasser, Saudi Aramco; R.S. Kuchinski and I. Zainaddin, Weatherford
Traditionally, brown field developments have often required the plugback and sidetrack of existing drain holes to target any nearby opportunities. With advances in drilling technology, there is a general preference to drill small-diameter wells because of the comparative cost advantage. In the recent times, this preference has led some wireline service companies to start to offer openhole formation evaluation services with slim tools with diameters in the 2-in. to 2½-in. range. At present, most traditional petrophysical measurements can be acquired using slim tools. In addition, several "specialized” measurements, such as cross dipole sonic, formation pressure testing, and resistivity imaging, can also be acquired. The use of battery and memory technologies has allowed deployment of these tools using a broader range of conveyance techniques for reduced risk in the entry of slim wells. The provision of slimhole logging services has created an opportunity to leverage these tools for the economic development of brown fields. Therefore, short horizontal sidetracks and well re-entries to test deeper horizons can be drilled and logged successfully. Saudi Aramco has leveraged these tools in its continued development of the giant Ghawar field. Some of the development projects are listed below: Some horizontal sidetracks with 3-in. hole sizes have been drilled under higher doglegs than was previously possible and logged successfully. It is now possible to run well completions in newly drilled wells that have a well control problem. A provision is made to subsequently log these wells with slim wireline logging tools. It is now possible to run a complete suite of wireline logs across some old wells that were previously completed without a full formation evaluation logging suite. Slimhole formation resistivity imaging services are now being provided to aid in identification of borehole breakout and fracture features that might affect the well productivity. Slimhole formation pressure testing has been acquired in slim wells to generate a pressure gradient, determine oil mobility, and define oil-water contacts.
Phase-based dispersion analysis for acoustic array borehole logging data
Said Assous and Peter Elkington, Weatherford; Laurie Linnett,BIOS Developments Ltd.
A phase-based dispersion analysis method for velocity (slowness) extraction from guided waves recorded by an acoustic borehole logging tool in a geological formation is presented. The technique consists of acquiring waveforms from an array of receivers distributed along the tool and constructing the dispersion characteristic by processing in the frequency domain and exploiting phase information to measure the travel time for each frequency component. The approach is nonparametric and completely data-driven and provides high-resolution estimates that do not rely on velocity guesses or assumptions regarding the type of modes. Results are free of the aliases and spurious modes that are characteristic of some prior approaches. Examples of dispersion estimation curves are presented using synthesized flexural waves and field data from wireline dipole sonic tools; results are compared with those from the weighted spectral semblance (WSS) and amplitude and phase slowness estimation (APES) methods to demonstrate the effectiveness and utility of the proposed method.
A Memory Cross Dipole Sonic Logging Tool and its Conveyance in Challenging Wells
Peter John Williams, Peter A.S. Elkington, Terry Mayor, and David Eccles, Weatherford;| Daniel Lester Long, Precision Energy Services
Sonic logs provide key data for seismic velocity models and have application in a broad range of drilling, completions, and production challenges related to rock deformation. A new small-diameter wireline-style sonic logging tool with memory capability reduces acquisition risk and extends the application of data into wells that are technically or commercially challenging for conventionally sized tools (such as slim and/or high-dogleg-severity wells and wells where logging out of drillpipe may be the only cost-effective evaluation option). Innovations in the design of the flexural wave transmitter, acoustic attenuator, and receiver assemblies allow compressional and shear velocities and shear anisotropy to be determined from a uniquely small package that is not constrained by wireline data transmission rates (and can therefore be combined with the microresistivity imager and other high-data-density tools without compromising logging speed). Performance is reviewed from operations around the world. Logs from shallow and deep reservoirs, including both conventional and unconventional reservoirs, demonstrate the robustness of the data over a broad range of common environments. The ability to accurately characterize slow formations (including from enlarged borehole intervals) is demonstrated, and minimum horizontal stress orientations inferred from the tool are shown to be consistent with independent analysis from image log data.
Flexural Wave Dispersion Analysis for Reservoir Characterization with a Small Diameter Cross Dipole Tool
David Eccles, Terry Mayor, Yibing Zheng, and Peter A.S. Elkington, Weatherford
Differences between observed and forward-modelled flexural wave dispersion characteristics in cross dipole sonic logging in homogeneous formations are useful for evaluating mud invasion and for differentiating between stress-induced and fabric-related anisotropy. In this paper we investigate the sensitivity of the dispersion effect to borehole size and mud slowness, and we show the importance of taking account of the tool's mechanical properties in the forward model—particularly when the tool diameter is a substantial fraction of the well diameter. We demonstrate that a new generation of small-diameter cross dipole tool has a small tool-effect in common hole sizes and extend the dispersion model results down to hole diameters less than 4 inches; we verify the calculations with real data sets acquired in sub 4-inch wells, as well as larger wells up to 12 inches in diameter. The results are also used to examine the size of dispersion corrections needed to calculate shear slowness in situations where low frequencies from the broadband transmitter are coupled relatively weakly to the formation.
Weatherford is a premier provider of acoustic logging services.
Weatherford provides versatile sonic and ultrasonic transmitter-receiver arrays that provide accurate monopole and cross-dipole measurements in a wide range of well geometries. Our efficient yet effective services can help you mitigate sand production and maximize oil and gas production potential throughout the life cycle of your asset.
Our Compact™ cross-dipole (CXD) tool helps you improve reservoir characterization and maximize reservoir productivity—even in complex well geometries.
The CXD tool is the industry’s only 2 1/4-in. monopole and cross-dipole sonic tool that can be deployed with or without wireline and through drillpipe for acoustic sonic logging in slow and fast formations. The tool records 96 high-definition waveforms to deliver compressional, shear-slowness, fast-shear azimuth, and Stoneley measurements for evaluating rock geomechanical properties.
Our Assure conveyance systems give you 10 distinct techniques to convey logging tools into open holes.
All Assure conveyance options work with our suite of unique Compact logging tools to obtain a full spectrum of logs, even in complex trajectories. The Assure systems enable you to get high-quality data in the most challenging wellbores while mitigating risks of lost-in-hole tools.