Leif Larsen

Inflow Predictions and Testing While Underbalanced Drilling

With increased interest in underbalanced drilling, including coiled tubing drilling, the importance of realistic inflow predictions and the potential for formation evaluation based on rate measurements is also receiving increased attention. This paper addresses these points by introducing new models for inflow predictions at various levels of complexity and accuracy for spreadsheet and calculator applications. The methods can handle both homogeneous and layered reservoirs, and essentially traps the expected formation response within a narrow range based on drilling speed and the ratio of vertical to horizontal permeability.

Wells Producing Commingled Zones with Unequal Initial Pressures and Reservoir Properties

A mathematical model is developed to determine pressure and flow-rate transients caused by differences in initial pressures of individual zones in multilayer no-crossflow systems, and effects on drawdown and buildup behavior are investigated. Skin factors are included through the use of apparent wellbore radii. Moreover, methods for estimating reservoir parameters from pressure transients prior to production are presented. A special method for estimating the flow capacity of each zone in two-layer reservoirs from long buildup tests is also included. 11 refs.

Determination of Skin Factors and Flow Capacities of Individual Layers in Two-Layered Reservoirs

Methods to determine skin factors and flow capacities of individual layers in two-layered reservoirs are presented. The methods are based on approximations derived for systems without crossflow, but can also to some extent be used to analyze early data from systems with crossflow. Limitations arise if the vertical permeabilities are of the same magnitude as the horizontal permeabilities, or higher. In such cases the methods presented in this paper can be invalidated by effects of crossflow. For drawdown and buildup analyses, the authors introduce both direct computational procedures and procedures based on trial-and-error plotting. Which procedure to choose in a given situation will depend on the smoothness of the data and the type of analysis being used.

Limitations on the Use of Single- and Multiple-Rate Horner, Miller-Dyes-Hutchinson, and Matthews-Brons-Hazebroek Analysis

This study presents methods to determine the range of applicability of Horner and Miller-Dyes-Hutchinson analysis for a variety of reservoir shapes, outer boundary conditions, and producing times. This concerns limitations on the end of semilog data caused by approximations of the drawdown transient, and not limitations on the beginning of such data caused by effects in or near the well bore. The results, based on derivatives of dimensionless pressures, also have some bearing on the use of drawdown type curves to analyze buildup data. Limitations on the use of standard methods to determine the distance to the nearest boundary in closed reservoirs, both for short and long producing times, also are investigated. Both Horner and Matthews- Brons-Hazebroek analysis have natural extensions from single- to multiple-rate buildup data. This leads to a formula relating the extrapolated pressure to the average reservoir pressure through a sum of Matthews- Brons-Hazebroek functions. 32 references.