Crossed dipole sonic logging data has traditionally been used in the openhole environment to:identify natural fracture systems and their orientation,evaluate far field stress data for 3D stimulation modeling, andseismic correlations and synthetic modeling. Materials presented inthis paper will show open hole and cased hole comparisons of flexural/shearwave slowness data and the anisotropy analysis in both fast and slowformations. The paper will show through-casing fracture identification examplesfrom the Cretaceous-Jurassic formations in Southern Mexico that have beenconfirmed with inflow analysis. The paper will also show applications ofthrough-casing anisotropy analysis combined with oriented perforating in theBurgos Basin in North Eastern Mexico. These techniques have resulted in lowerbreakdown pressures on stimulation treatments due to minimizing near wellboretortuosity. 2D and 3D analytical and finite-difference wave propagationsimulators have been developed to verify the open-hole and cased-holescenarios. The finite-difference simulations are used as a predictive tool toidentify cased-hole conditions that are either favorable, or unfavorable forcased-hole dipole acquisition. Introduction Dipole logging requires the propagation of a low frequency out-of-phaseflexural wave that is detected by the acoustic receivers on opposite sides ofthe logging tool. To accomplish this symmetry is required. The wireline dipolesonic tool must be centralized in a near round borehole. For through casingdipole logging, the casing should also be centralized, and the material in thecasing-formation annulus must be radially uniform. The effects of boreholeovality, tool centralization, or casing centralization on waveform propagationare illustrated in Fig. 1 for a 1.5 kHz center frequency flexural wave. Lowerfrequency flexural/dipole transmitted pulses have longer wave lengths, thanhigher frequency flexural wave propagation, thereby slightly reducing the phaseshift due to borehole geometry effects. An elliptical borehole is common indeviated wells due to eccentralization of the drill string and bottom holeassembly. Acquiring crossed dipole sonic data at low frequency and in two axes(X and Y) often minimize these environmentally induced effects. The crossed dipole sonic logging tool is frequently run open hole in what isreferred to as a "quad-combo" (natural gamma ray, eccentered dual spacedneutron, density, dual induction, or dual lateralog with appropriate standoffs, centralized dipole sonic, and navigation tool). One such logging toolstring is configured such that the X-dipole measurement is aligned with thedensity pad, which due to gravity effects will seek the low side of theborehole in deviated well conditions. Therefore, the X dipole measurement maybe affected by tool positioning effects in the angle build sections of deviatedwellbore. The Y-dipole measurement is orthogonal to the density pad and in poorborehole conditions often provides quality shear wave slowness data. Aspreviously discussed, centralization is required, but in certain bore holeconditions this may not be operationally possible. Acquiring crossed dipoledata through casing is a viable option, provided the borehole conditions arefavorable. Unfavorable conditions for through casing dipole logging areexcessive washouts, poor radial placement of cement, lack of casingcentralization, and poorly consolidated formations. Advanced waveformprocessing, such as slowness anisotropy analysis, which is used to determinethe fast and slow shear wave travel times and their corresponding orientationrequires that a navigation device be run simultaneously with the dipole sonictool.1 In open hole logging conditions magnetometers andaccelerometers are utilized. In deviated cased hole logging conditionsmulti-axes accelerometers can be used. In near vertical cased hole loggingconditions a gyroscope is required. Anisotropy analysis can be performedwithout tool navigation data, to determine the magnitude of the anisotropy, butthe orientation of the fast and slow shear waves is referenced to the toolface, which can rotate while logging. This is frequently done in geologicconditions where the anisotropy is know to be a result of natural fracturing, and fracture orientation is not desired.

Proposal Based on local experience, a well-accepted work flow or set of best practices has been developed for optimizing stimulation treatments in the Burgos Basin. Recently, these best practices have been enhanced by combining stress field orientation and gyroscopically oriented wireline perforating. Orienting perforations in the direction of maximum horizontal stress has greatly reduced near wellbore tortuosity and friction in hydraulic fracturing treatments. The result has been improved proppant placement resulting in higher proppant conductivity and increased production. The best practices for optimization of the stimulation design and economic modeling include many steps. 1,2,3,4,5,6,7,8,9,10 The candidate selection process evaluates the net-to-gross sand thickness ratio, reservoir pressure, and permeability for each zone. The net-to-gross ratio provides information on productive and non-productive fracture height, which is needed for inflow analysis. The reservoir fluid, pressure, and permeability of the formation are vital for determining the fluid leakoff/fracturing fluid rheology requirements and required fracture conductivity. Geological and geophysical data are reviewed to identify potential reservoir boundaries such as faults or pinch-outs that could impede hydraulic fracture propagation. The vertical stress profile between the zone to be treated and the underlying and overlaying formations is used in 3D fracture simulators to evaluate the fracture height (and any possible unwanted outof- zone fracture height) versus fracture half-length and proppant concentration. To implement the oriented perforating enhancement to the best practices crossed dipole sonic anisotropy analysis is used to determine the far-field stress orientation and magnitude combined with the six electrode dipmeter for orientation and ovality visualization. Borehole breakout analysis and anelastic strain recovery of whole cores can provide near-field stress orientation data. These factors are then used to determine optimum perforation direction. In this paper, several case histories will be presented comparing the results of stimulation treatments using the normal practices and traditional perforating methods versus stimulation treatments using the same practices but incorporating oriented perforating. Stress Orientation and Borehole Breakout The near field stress orientation can be determined from borehole breakout analysis, which requires at a minimum multi-axis calipers and borehole orientation data. In both vertical and deviated wellbores, borehole breakout analysis from X-Y caliper data can sometimes provide suitable information. The borehole ovality can also be a result of the drill string and its rotation or sliding on the low side of the borehole in deviated well conditions. Both of these phenomenon can result in a key shaped borehole. If only X-Y caliper data is used, the pipe groove/key shaped borehole can be interpreted as borehole ovality. These conditions can generally be identified with the long axis of the borehole, constantly aligned with high side-low side of the borehole. Multi-axis calipers with more than X-Y measurements (Fig. 1) provide additional data which can enhance the borehole geometry-borehole break out analysis. Borehole imaging data (Fig. 2), ether ultrasonic or electrical, have much greater radial and vertical sampling than multi-axis caliper data. The imaging data not only provide high resolution borehole geometry data, but yield essentially a picture of the detailed bedding. Fractures can readily be identified from imaging data.

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Electric logs and borehole imaging were used to build a geomechanical model to predict wellbore instability during drilling and to optimize casing designs and completions to control sand production in the Burgos Basin. This paper describes how geomechanical models can explain several problems in drilling and completion during the development of some of the fields in Northern Mexico. The total stress tensor model, the pore pressure model, and the mechanical properties model are discussed. Validation of the model is a critical step before it can be applied to design new wells. The geomechanical model was used to design a new well and to optimize drilling, completion, and production techniques for the reservoir. The model was used to optimize the placement and orientation of perforations, evaluate proposed hydraulic fracturing designs, and select the critical draw-down to produce a well. Actual drilling, completion, and production events for the new well were analyzed, and conclusions about how the geomechanical model supported the complete design are also included in this paper. Introduction Several studies worldwide have confirmed that the optimization of non productive time related to borehole instability while drilling, the determination of the preferential permeability in naturally fractured reservoirs, the integrity of seals in geological faults, sand production potential, reservoir compaction and casing damage, are controlled by the geostatic in situ stresses, the pressure of the fluids in the pore spaces and the mechanical properties of the rocks. A geomechanical model for the field was built based on information from conventional and electric imaging logs in addition to the drilling information of the first exploratory well, F-1, drilled in the field. The model was validated predicting breakouts in the F-1 well and comparing them with rock failures observed in the caliper log, breakouts observed in the electric imaging log and with drilling problems related to wellbore instabilities. The geomechanical model for the field predicts well the observations and problems identified in the F-1 well during the drilling, completion (hydraulic fracture) and initial production of the well. A wellbore stability analysis during drilling and completion was performed for the F-1 well to predict the mud weight requirements during drilling to prevent large breakouts/washouts or lost of circulation problems and the required borehole pressure to prevent sand or formation flowing during the production phase. Furthermore, the lessons learned from F-1 were successfully applied to drill, stimulate and produce a new well, F-101. Geomechanical Model The project started collecting all the information related to planning, drilling and completion of the F-1 well. This well was drilled as a directional J-shape well to reach the final objective in the Jackson Formation, as presented in Figure 1. General information of the Field was reviewed (including surface seismic and maps), the structural model, standard and advanced wireline logs including dipole sonic and images acquired in the F-1 well, drilling and completion information (including daily reports, mud weight reports, well design schematic, leak off tests and Minifrac tests), pore pressure measurements in the reservoir, well geometry and formation tops.

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