Effective Completion and Reservoir Management With Well Logs
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 144774, ’History Matching and Production Forecasting With Logs: Effective Completion and Reservoir-Management Tools for Horizontal and Vertical Wells,’ by Carlos F. Haro, SPE, Occidental Oil & Gas, prepared for the 2011 SPE Annual Technical Conference and Exhibition, Denver, 30 October-2 November. See SPE Res Eval & Eng, October 2012, page 596.
Simulation history matching is a time-consuming task with many unknowns, and it yields several plausible answers. Scale differences in the data frequently obscure results, precluding effective application in completion strategies. Good history matching does not guarantee accurate production forecasts. Reliable predictions, required for well planning, depend on the ability to reduce uncertainties and to find consistent and timely solutions. Well logs can provide appropriate conditioning data for history matching and managing the reservoir.
Introduction
Electrofacies, absolute and relative permeabilities, and capillary pressure data imprinted on well logs can be linked mathematically with irreducible water saturation (Swi). The well logs are at the correct scale for completion designs. They facilitate scaling up, honoring rock and fluid properties and the physics of flow. Logs are snapshot measurements, amenable to conversion into dynamic forecasting tools by use of flow and pressure equations. This concept enables building synthetic production logs over time to calculate the production decline.
Petrophysicists deliver static quantities such as clay volume, porosity, water saturation (Sw), and permeability (k). Unfortunately, they do not generate parameters such as connectivity of well laterals, recovery, or dynamic data in general. Techniques detailed in the complete paper can alleviate this basic gap.
Zero-dimensional material balance usually is applied to whole reservoirs, not to single wells. The customary argument is that wells are not isolated and they respond to the influence of nearby wells, which masks results. Despite this limitation, material balance is used in horizontal and vertical wells by assuming that each well is a tank with fixed dimensions and distinctive petrophysical properties and produces from only its own drainage area. This method computes the main reservoir parameters sequentially and it establishes reference profiles and values (i.e., base case). Then, the observed differences can be interpreted as external interferences or operational changes over time, which can be quantified by use of superposition. Also, a well will indicate its intrinsic initial capacity before being affected by other wells. The arrival of interactions between wells requires time. The period after the infinite-acting period can serve to calibrate well deliverability obtained from openhole logs. This procedure determines the constituent parts of a whole reservoir quantitatively (every zone, every well), while the simulation strategy is the opposite: knowing the total, it infers the parts. The latter, frequently an inverse problem, leads to several feasible answers.