Wellbore stability analysis for horizontal drilling required data over 5,000-ft interval

To effectively access the primary target with a horizontal wellbore, Laredo Petroleum needed to drill through multiple targets distributed over an extensive interval. A detailed analysis of rock mechanical and petrophysical properties was required over an interval of 5,000 ft to determine the optimum operating parameters, such as maximum and minimum allowable mud weight along the well trajectory. Wellbore stability presented several challenges to drilling the lateral, and Laredo wanted to maximize the representation of variable rock properties with minimum outlay.

TerraTek HRA provides geomechanics based facies analysis

After consideration and consulting with Laredo Petroleum, Schlumberger proposed TerraTek rock mechanics and core analysis services to address the challenge. HRA was used to evaluate the variability of log measurements as a function of depth, to create a pattern of these responses, and identify the occurrence of identical data patterns along the interval of interest. Analysis showed heterogeneity at log scale and discriminated zones of consistent mechanical behavior within heterogeneous media.

Before drilling, a regional HRA reference model was developed based on a series of previously existing offset wells, including those that had been characterized for mechanical properties. Rock classes were subsequently assigned to the vertical section of the subject well after tagging to the reference model. Strong compliance between the deeper intervals and the reference wells indicated good correlation between the rock classes and strong similarities in material properties, eliminating any need for further sampling. Shallower intervals showed poor compliance, indicating the presence of new facies that required coring and laboratory characterization.

Correlation of hRa results with offset wells reduced coring interval to 1,000 ft

TerraTek services enabled Laredo Petroleum to analyze a framework into which well properties are populated, allowing nonbiased, representative sampling for better, more applicable results. The coring interval was reduced from a potential 5,000 ft to 1,000 ft. An optimum number of locations for sidewall core plugs were selected, ensuring adequate sampling of all facies to obtain the data required for addressing stability and mud weight issues. After large-diameter and conventional rotary coring tools were used to sample, a multipath testing suite measured both vertical and horizontal mechanical rock properties. A mud weight window was developed for each of the facies identified, enabling Laredo Petroleum to drill the lateral successfully with an 80% shorter coring interval. The facilitated decision suggested by HRA that coring the 300-ft-thick interval was unnecessary saved Laredo Petroleum hours of rig time and approximately USD 250,000.