Multilayer Reservoir Testing with Multiprobe Wireline Formation Tester.

Summary.

Four multiprobe wireline formation pressure transient tests were performed in a well in the Thamama formation. The main purpose of the tests was to estimate vertical communication across what were perceived to be thin, tight layers. The tests were unique because they had sink and horizontally offset probes, and two vertical probes - the farther one being almost ten feet away from the sink.

The downhole tests were complemented by extensive core measurements of porosity, vertical and horizontal permeabilities, and other petrophysical properties. The cores and the wellbore images obtained through the formation micro imager were depth matched. A reservoir model comprising 30 layers was used to analytically model the tested region for pressure transient propagation. The layer model was constructed based on the geological description, openhole logs, and the resistivity images. The data from the wellbore multiprobe interference tests were used to estimate the layer horizontal and vertical permeabilities using a nonlinear least-squares estimation method. The permeabilities from cores, pretests, and multiprobe tests were found to compare favorably. In addition, the pretest permeabilities along the wellbore, which correspond to endpoint effective permeabilities in the filtrate invaded region are within 50% of the core values. This suggests a weakly wet formation. The following results have been deduced from our study:

  • Vertical communication across zones of interest; - Horizontal and vertical permeabilities on probe spacing length scales;

  • Integration of high-resolution wellbore images with multiprobe measurements;

  • Reconciliation of core and log data with multiprobe pressure transient tests for new insights into vertical continuity.

Introduction

This paper presents the interpretation of four multiprobe pressure transient tests conducted at four locations along the wellbore with Modular Formation Dynamics Tester (MDT) in Well X in the carbonate Thamama reservoir. The multiprobe formation tester (MDT) is shown in Fig. 1 and is described in detail by Zimmerman et al. A four-probe configuration, as also shown in Fig. 1, that consists of sink and horizontal probes (dual-probe module) and two single vertical-probe modules, was used to perform these transient tests. The sink-observation probe spacings are 2.3 ft for the first vertical probe (V1) and 10.3 ft for the second one (V2) as shown in Fig. 1. For each transient test, the pressure distribution in the formation was created by producing (withdrawing) fluids through the sink probe with the pumpout module or one-gallon sample chamber. The pumpout module consists of dual chambers that alternate the pumping of formation fluids into the borehole. The reciprocating piston pumps hydraulic oil into the pump-out module displacement unit.

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