Michael S. Bittar

Three-dimensional simulation of eccentric LWD tool response in boreholes through dipping formations

We simulate the response of logging-while-drilling (LWD) tools in complex thee-dimensional (3-D) borehole environments using a finite-difference time-domain (FDTD) scheme in cylindrical coordinates. Several techniques are applied to the FDTD algorithm to improve the computational efficiency and the modeling accuracy of more arbitrary geometries/media in well-logging problems: (1) a 3-D FDTD cylindrical grid to avoid staircasing discretization errors in the transmitter, receiver, and mandrel geometries; (2) an anisotropic-medium (unsplit) perfectly matched layer (PML) absorbing boundary condition in cylindrical coordinates is applied to the FDTD algorithm, leading to more compact grids and reduced memory requirements; (3) a simple and efficient algorithm is employed to extract frequency-domain data (phase and amplitude) from early-time FDTD data; (4) permittivity scaling is applied to overcome the Courant limit of FDTD and allow faster simulations of lower frequency tool; and (5) two locally conformal FDTD (LC-FDTD) techniques are applied to better simulate the response of logging tools in eccentric boreholes. We validate the FDTD results against the numerical mode matching method for problems where the latter is applicable, and against pseudoanalytical results for eccentric borehole problems. The comparisons show very good agreement. Results from 3-D borehole problems involving eccentric tools and dipping beds simultaneously are also included to demonstrate the robustness of the method.

Numerical Modeling of Eccentered LWD Borehole Sensors in Dipping and Fully Anisotropic Earth Formations

Logging-while-drilling (LWD) borehole sensors are used to provide real-time resistivity data of adjacent earth formations for hydrocarbon exploration. This allows for a proactive adjustment of the dipping angle and azimuth direction of the drill and, hence, geosteering capabilities. The analysis of borehole eccentricity effects on LWD sensor response in full 3 3 anisotropic earth formations is important for correct data interpretation in deviated or horizontal wells. In this paper, we present a cylindrical-grid finite-difference time-domain model to tackle this problem. The grid is aligned to the sensor axis to avoid staircasing error in the sensor geometry but, in general, misaligned to the (eccentered) borehole/formation interface. A locally conformal discretization is used to compute effective conductivity tensors of partially-filled grid cells at those interfaces, involving an isotropic medium (borehole) and a full 3 3 anisotropic medium in general (dipped earth formation). The numerical model is used to compute the response of eccentered LWD sensors in layered earth formations with anisotropic dipping beds.

Modeling of EM logging tools in arbitrary 3-D borehole geometries using PML-FDTD

We discuss the numerical modeling of logging-while-drilling (LWD) tools for hydrocarbon exploration in arbitrary three-dimensional geometries using a new finite-difference time-domain (FDTD) scheme in cylindrical coordinates. Two locally conformal FDTD (LC-FDTD) schemes are employed to simulate eccentric LWD tools in realistic logging environments. An anisotropic perfectly matched layer absorbing boundary condition extended to cylindrical coordinates is incorporated in the FDTD method to simulate unbounded geophysical formations. Frequency-domain data are obtained from the time-domain results using a ramp-modulated sinusoidal source and an efficient early-time extraction algorithm. The FDTD simulations are validated against both numerical mode matching and pseudoanalytical approaches and show very good agreement.

Real Time Proactive Optimal Well Placement using Geosignal and Deep Images

Optical fluid analyzers have been used in wireline formation tests for real-time downhole fluid analysis during pumpout tests for over a decade. Based on conventional optical spectroscopic methods, they separate broadband light into its constituent wavelengths via notch filters or multichannel grating spectrometers. A few narrow wavelength constituents are then detected and mathematically recombined to yield an answer product. Complex hydrocarbon fluids have many overlapping spectra and are optically active over a wide range of optical wavelengths. Consequently, accurate analyte detection in hydrocarbon fluids generally requires analysis of a large number of wavelengths over a large spectral region. The performance and range of detectable analytes of conventional optical fluid analyzers is band-limited. Of all available spectra from visible to nearand mid-infrared, only a small fraction of spectral data is used. In addition, the splitting of the optical beam into its wavelength constituents typically decreases signal-to-noise ratios (SNR) by orders of magnitude thereby limiting the accuracy, sensitivity, and viable ranges of the answer product. A new downhole optical sensor platform has been developed for downhole in-situ fluid analysis based on multivariate optical computing (MOC) technology. Historically developed for other markets, MOC is a well-established tool that combines chemometrics and pattern recognition with the power of optical computing. The heart of this new optical sensor platform is an optical component called the ICE CoreTM integrated computational element. The ICE Core sensor is analogous to the processing chip of a PC and performs calculations literally at the speed of light within the multivariate optical computer. Each ICE Core special multilayer optical element is encoded with a pre-designed multivariate regression vector specific to an analyte or property of interest. These optical elements are typically very broadband and may have a response that extends from 400 nm to 5000 nm. The wide bandwidth of these optical elements combined with their intrinsic, high etendue SNR advantage enables laboratory-grade optical analyses downhole. The compact and passive nature of the ICE Core sensors results in high reliability. A multivariate optical computer may consist of many different ICE Core sensors designed to detect many different analytes or properties. The downhole optical sensor platform in this study can have 20 (or more) different ICE Core sensors per MOC. This platform has been under field trial qualification for over a year using a step-by-step process with methane (C1) ICE Core sensors as the primary validation analyte. In this paper, the results of three different downhole pumpout field trials are presented. After reviewing the fundamental principles of MOC and ICE Core technology, the field trial validation process is described. Results showing downhole ICE Core measured methane analyte concentrations vs. time are presented and compared with other downhole sensor data. ICE Core measured concentrations are also compared with independent laboratory test results. The results demonstrate the downhole viability of the optical platform and the sensitivity associated with the ICE Core detection method. FIELD DEMONSTRATIONS OF ICE CORE TECHNOLOGY ICE Core Website

Drilling a Better Pair: New Technologies in SAGD Directional Drilling

The precise placement of well pairs is one of the most-crucial factors in the successful execution of a steam-assisted-gravity-drainage (SAGD) drilling program. A SAGD drilling program includes placing the producer well relative to the reservoir boundaries and twinning the producer with the injector well accurately. Delivering on these high expectations in unconsolidated formations (e.g., the McMurray oil sands in Canada) requires a strong focus on technological innovation. A common practice in drilling SAGD wells in northeast Alberta is to drill lateral SAGD pairs with conventional, steerable mud motors and logging-while-drilling (LWD) resistivity measurements. Although this combination has delivered success, certain limitations exist in terms of wellbore quality and placement. At a demonstration project by a major oil company, several industry firsts were implemented successfully, including a combination of the newest and most-cutting-edge directional, measurement, and LWD technology. The keystone of these industry firsts was the application of a soft-formation-modified, point-the-bit rotary-steerable system (RSS) used on 20 horizontal wells. Combined with an ultradeep azimuthal resistivity sensor, the RSS provided precise geosteering along the bottombed boundary in the producer wells, resulting in improved reservoir capture and characterization. More on-bottom time enabled more-efficient drilling and reduced well costs significantly. Highly smooth liner runs reflected the lack of tortuosity in the wellbore, made possible by the rotary bottomhole assembly (BHA). Improved directional control made uniform well separation possible between lateral pairs, thereby reducing the risk of hot spots and short circuiting during SAGD operations. The use of an even-walled power section above the RSS increased the bit rev/min for improved BHA responsiveness while minimizing casing and pipe wear. Overall, the results and lessons learned from the demonstration of these new techniques provide a clear indication of the progressive future of directional drilling in SAGD.

3D simulation of LWD directional resistivity tool response using FDFD potential formulations

*u Summary The authors present a novel finite-difference frequencydomain (FDFD) method for simulating the response of a logging-while-drilling (LWD) directional resistivity tool in three-dimensional borehole environments. This new method is based on the numerical solution of the boundaryvalue problem of the electromagnetic coupled potentials using the finite-difference approximation in a cylindrical coordinate system. Numerical simulation examples are provided to show the validity, accuracy, and efficiency of this new numerical formulation. All the results obtained by this method agreed well with 1D analytical, 2D numerical mode matching (NMM), and 3D FDTD results. The FDFD method is used to show environmental effects on a tilted antenna LWD tool.

Borehole And Invasion Effects of New Asymmetric Array Induction Tools

The equations to evaluate borehole and invasion effects of Halliburton’s new asymmetric array induction tools, ACRtTM and H-ACRtTM, have been developed according to the geometric factor theory of induction logging. To use these equations, we first examined the borehole effects. The numerical simulation confirms that when the borehole size is less than or equal to 10 inches, the three long spacing subarrays are not usually affected by the borehole conditions (mud, borehole size, and tool eccentricity). Then we investigated the invasion effects. For the fixed invasion depth and borehole conditions, the invasion effect is approximately a linear function of the conductivity difference between invaded-zone and virgin formation; for the fixed conductivity difference between the invaded-zone and bed formation, the invasion effect is a non-linear function of the invaded depth. We can also use the equations for estimating the required depth of invasion for the given log curve separation, or for estimating the maximum curve separation for the given depth of invasion.

Response of tilted-coil antennas in multicylindrically layered media

We analyze the response of tilted-coil antennas in multicylindrically layered media. The loop antennas have fixed radial size of 4.5 [in]. Both the axial and azimuthal angles of the antennas can be changed. The transmitter antenna is placed at the position z=0 [in]. The first and second receiver antennas are placed at the position z=30 and 24 [in], respectively. The operating frequency is 2MHz. We study the response of this tool in multilayered formations. Both a pseudo-analytical formulation extended to multicylindrically layered medium, and a full numerical formulation based on the finite-difference time-domain (FDTD), are used to analyze this problem and for cross-validation. The FDTD method here employs a three-dimensional (3D) cylindrical grid to better conform to the logging tool geometry.