To complete the Marcellus shale's horizontal wells simply and cost-effectively, operators typically use geometric perforation designs in order to prepare for hydraulic fracturing. With this technique, perforation clusters are placed at equidistant points along the lateral. However, microseismic monitoring shows that this type of stage selection often distributes hydraulic fracturing treatments unevenly. The fracture treatments propagate to the lowest-stress intervals, leaving a large number of perforations under stimulated or simply unstimulated. In an attempt to improve on this technique, a study was performed in which wells using an engineered perforation design were compared against offset wells that had a geometric perforation design. For the wells employing an engineered design, an acoustic scanning tool was deployed on wireline and mechanical rock properties were obtained along the length of the productive lateral. The critical well information, including in situ stress, lithology, Young's modulus, and Poissons Ratio enabled engineers to create custom staging and perforating designs. These designs were optimized to provide more consistent stimulation along the entire lateral, and lower breakdown and treating pressures. The final result of using the engineered perforation design was a significant increase in production when compared to conventionally completed wells. During the stimulation treatment of the engineered perforation design, there was a significant drop in the average treating pressures during fracturing when compared to geometric offsets. This was due to several factors including the fact that perforations targeted lower stress intervals. In addition to lower pressures, an elimination of premature job terminations or "screen-outs" was seen. This occurs when pressures increase to such a degree that the stimulation treatment cannot continue within acceptable pressure ranges. Previous treatments in offset wells yielded a 35% screen out rate which resulted in significant lost time and additional costs. The process and production results of wells completed with geometric perforations to wells with engineered perforations.

Perforating a horizontal well in the Marcellus shale is typically performed using bare essential technology. Simple rules-of-thumb for perforation cluster spacing and interval length are applied, most likely derived by trial and error, and rarely validated by methods such as production logging and microseismic monitoring. Conversely, a perforating method that is gaining notoriety is an engineered approach in which perforation clusters are placed in each fracture interval of rocks that have similar properties. The reasoning for this method is that it will ensure equal injection rates and volumes of the hydraulic-fracture treatment into each of the perforation clusters; maximizing reservoir contact and production from each cluster. The completion engineer might base the perforation design on gamma ray measurements with additional support of a mud log. While these measurements add some clarity to the perforation design, there is no evidence that either of these measurements have a direct impact on the breakdown stress of the rock, which is the primary driving force that dictates flow distribution of a hydraulic fracture treatment. Current logging technology does allow us to measure compressional, fast-and slow-shear, and Stoneley slowness waves in 3D along the horizontal cased borehole. These data can then be used to calculate stress and provide a stress profile along the lateral, which can provide an accurate basis for completion design. Fluid distribution is predicted by way of both basic orifice-flow calculations and 3D hydraulic-fracture models (using actual stress data) and then verified using observations from microseismic monitoring results. This paper presents a field case in which production improved using the perforation design method described above vs. one using conventional geometrically spaced perforations. In this case study, the operator made the new design technique part of their standard completion program.

Published in Petroleum Transactions, AIME, Volume 204, 1955, pages 1–6. Abstract The development process for the use of radioactive tracers as a means of locating zones of permeability is discussed. The general techniques for the safe handling of radioactive materials is given as developed by the Lane-Wells Co. and Well Surveys, Inc. The problems and successes with tracers in waterflood systems, oil and gas injection profiles, fracture sand tracing, squeeze cement tracing, lost circulation, and cement top location are discussed and illustrated. Introduction The exact location of the permeable zones lying within the productive horizon has been a major problem faced by the petroleum engineer for decades, and it has been a problem which has seldom been solved with certainty. Reservoir engineers usually have to incorporate a question mark in their estimates of future reservoir performance because of blanks in the core data. Although the use of radioactivity or electrical logs for the estimation of porosity has been of great assistance in furnishing a record for the reservoir engineer, this application of logging data has not completely solved the problem. In short, the industry needs an in-situ well surveying method which can locate and estimate the permeability of the zones existing within a given pay section. The initial development work with radioactive tracers has been towards filling the need for permeability information. Progress to date permits the location of permeable zones with a qualitative estimate of theirrelative importance with respect to permeability. The calibration of the method is still incomplete, but present development work on tracer preparations, borehole effect correction factors, and instrument limitations give a promise of quantitative "permeability profiles" in the near future. The development work on the radioactive tracer method discussed here began several years ago in the laboratories of Well Surveys, Inc., in Tulsa.