LATEST GENERATION LOGGING WHILE DRILLING SONIC TOOL: MULTIPOLE ACOUSTICS MEASUREMENTS IN HORIZONTAL WELLS FROM OFFSHORE WEST SOUTH AFRICA

摘要

Logging while drilling (LWD) technology hasprogressed swiftly in recent time to address the need forsaving rig time, making real-time informed decisionsfor drilling efficiency and risk management, andaccurate well placement. LWD sonic measurementsprovide information for timely analysis of boreholestability, drilling optimization, and assisting with porepressureprediction and well-to-seismic tie. Most ofthese applications have relied on the measurements offormation compressional slowness due to the difficultyin obtaining shear slowness in the LWD environment,especially in unconsolidated formations. Formationshear slownesses, measurable by logging while drillingsonic technology, can complement compressionalmeasurements for advanced applications (AVOanalysis, geomechanics, completion, lithology, andhydrocarbon detection). This paper will demonstrateadvances that have been made in new LWD sonic toolswith the evaluation of both shear and compressionalvelocity measurements; the new technology was usedfor two horizontal wells in West South Africa.A new LWD sonic tool has been developed to addressthe challenges in obtaining shear measurements inunconsolidated formations. The new technologydesigned for robust measurements of compressional andshear slownesses, regardless of the formation velocity,enables advanced applications from sonic data. The toolcan acquire multiple acoustic modes (monopole andquadrupole) with 48 sensors (4 azimuthalmeasurements at 12 axial positions). Its large acousticaperture and short inter-receiver spacing enhances thequality and resolution of processed slownesses. With itspowerful computing capability, the tool enables morecomplex processing downhole, leading to broaderapplications in real time.Field test data acquired in two horizontal wells in WestSouth Africa show that the tool can acquire high-qualitywaveforms over a wide frequency band, providingreliable compressional and shear slownesses in theformations penetrated by the boreholes. Formationcompressional and shear slownesses from the monopolewaveforms were transmitted in real time. Shear dataare present in the monopole dataset, and formationshear slowness was extracted from the monopolewaveforms in addition to the quadrupole waveforms,when possible. Monopole shear measurements are notcontinuous throughout the logged interval because ofvariation in formation types (slow or fast relative tomud speed) but quadrupole waveforms enabled acontinuous shear measurement. When possible toextract shear slownesses from both monopole andquadrupole data, some differences were discoveredbetween the two datasets. The difference betweenmeasured shear slownesses from monopole andquadrupole waveforms suggests acoustics anisotropy.In these environments, shear anisotropy in thehorizontal well is expected from the large differencebetween vertical and horizontal stress, as well aslayering (from the horizontal or near horizontal shalelayering).With high-quality waveform recording, real-time datadelivery, and advanced processing, this new LWDsonic technology provides robust compressional andshear slowness data, opening new frontiers for LWDsonic applications.