Well Completion in Directional Wells with Emphasis on Log Analysis, Petrophysics, and Core Mineral Analysis
Authors: Hayatdavoudi A. 
Published: December 2007

In this paper, we present a comprehensive methodology and several case histories that show the results of the proposed methodology for completing a well in highly laminated, dirty, and unconsolidated sands. The problems associated with the standard well completions are many, notable among which are the failure of perforation tunnels, unsustainable production, rapid well sanding, and the subsequent implementation of expensive sidetracking, work-over, and well maintenance programs.

Our proposed methodology uses a multidisciplinary approach to the problems at hand. We carry out the task of evaluating and characterizing the reservoir rock by linking all the available data, which we reduce to a single, calculated Perforation Index, αH, HPI. The data needed for a successful completion using our method are: (a) Well Logs (Dipole Sonic, Neutron Porosity, Density Porosity or Epithermal, Gamma-ray, Resistivity (shallow, medium, and deep), SP, Caliper, and Cable Tension, (b) Petrophysics (sidewall core analysis, grain size analysis, pore distribution, vertical permeability, horizontal permeability, helium porosity, water-oil-gas saturation, etc), (c) Mineral analysis (mineralogy of matrix, cement, and lamination X-ray Diffraction-bulk and clay, X-ray Fluorescence (oxide analysis), Thin Section Analysis, SEM Analysis-at 1 to 200 micron scales), (d) Geology (maps: structural, stratigraphic, topographic, gas-oil-water contacts, paleo descriptive log, etc.), (e) Drilling (offset well bit records, daily mud recaps, casing programs, cementing procedures, drill time logs, hydraulic program, well bore geometry, and planned directional trajectories and the final survey), (f) Offset Well Production, if any (offset well tests, daily fluid rates and decline, tubing size and type, well shut-in and well flowing pressure, average reservoir pressure, choke size, production casing program, separator pressure, composition of fluids, all reservoir stimulation and completion information (completion fluids, packer fluid, acidizing (if any), fracpack (if any), water or gel pack (if any), all gravel pack-screen or slotted liner completion information, all perforation information (number of shots per ft, type of gun, penetration, phasing, the certified shot core flow efficiency test, the certified estimates of perforation tunnel length and perforation entrance diameter, etc.), water injection program and injectivity tests, and mud or produced fluid disposal program.

The above-mentioned data is rather comprehensive. However, a completion team may incorporate some of the information in this list as a menu checklist, as backup, or as alternate redundant information for workflow and teamwork. We link items (a) through (f) to each other and arrive at a single value called αH, H-Perforation Index (HPI). The plot of HPI vs. Pay Zone Depth indicates, within a depth window and HPI Scale window, where to perforate and where to skip perforation in unstable and poor quality intervals.

The results of this completion methodology proved fruitful (approximately nine hundred bbls of oil and eight MMCF of gas per day) for a well completed according to our recommendations in comparison with standard well completion practices in the same field which had resulted in total loss of one well and only a marginal production from another. In another case, a comparison of the first two years of production data from three wells completed without our prescribed workflow and the production data from a well drilled and completed with our proposed workflow procedure showed a several-fold increase in production.

Based on the field production results and our analysis, we have concluded that a calculated αH, HPI, can lead to a selective and profitable completion in the highly laminated, dirty, and unconsolidated sands.