This paper describes numerical simulation studies designed to investigate the behavior of horizontal wells that intersect high permeability layers sandwiched between two lower permeability layers. The paper investigates the pressure transient behavior of 1) purely horizontal wells drilled in the middle layer and 2) slant horizontal wells that intersect all three layers, as the permeability of the high permeability layer is varied. A previous paper1 (SPE 88704) focused on late time interference effects and radial composite behavior caused by a limited high permeability Super-K layer. This study focuses on the early time dual permeability effect and its impact on recognition of conventional horizontal well diagnostic derivative slopes. The horizontal well simulations show a dual permeability effect as the contrast between the high permeability layer and the adjacent layers is increased. The vertical radial flow regime is seldom visible and masked by wellbore storage effects. Interestingly, what is observed however, is a plateau (or sometimes valley) caused by the dual permeability effect followed by a transition to horizontal radial flow regime. This may be explained as a combined effect of recharge and linear flow in the lower permeability layers. The plateau (or a valley) caused by the dual permeability effect, can easily be confused as representing the vertical radial regime. Similarly, the transitional data prior to horizontal radial flow, which includes the dual permeability effects, can be incorrectly analyzed and lead to misleading results. This paper will demonstrate the increased complexity of the pressure transient behavior when the well is slanted through all layers while intersecting the high permeability layer. Introduction The ability of horizontal wells to provide large areas of contact with the reservoir makes horizontal wells more suitable for the efficient recovery of oil, especially from thin reservoirs. Thus, horizontal wells have become the norm, rather than the exception, for the exploitation of oil and gas reservoirs, especially when the reservoir is underlain by an acquifer21. Pressure transient testing has become the standard means of evaluating the effectiveness of horizontal wells, as well as characterizing the reservoir being drained by the horizontal well. Several studies have proposed analytical solutions and also methodologies for analyzing horizontal well tests3 2–65. Some of these analysis techniques use sequential straight line methods based on the identified flow regimes, to estimate reservoir and well parameters from the tests. For automatic parameter estimation using the whole test data, non-linear regression techniques are used. Mattar and Santo7 have proposed an analysis technique based on a combination of the two methods6.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper presents a successful multi-well test analysis approach to identify and locate the geological feature(s) responsible for inter-reservoir communication between Lower and Upper reservoirs in ABQQ field. The study resulted in locating and identifying the nature of conduit(s) responsible for the direct communication between Lower and Upper reservoirs. Conductive fault(s) is/are observed repeatedly by five offset wells and clearly running between the two reservoirs. The location of the fault/faulted zone was predicted via an integrated approach including analyzing all the wells in the vicinity of the area under study and reviewing the drilling, logging and production data.An interference test was conducted after producing Lower injected water from Upper reservoir. The test indicated a direct communication through five hundred feet of nonreservoir formation between the two reservoirs.Many hydrocarbon bearing reservoirs are faulted, yet little information is available about the actual physical characteristics of the faults. Loss circulation while drilling horizontal wells, along with production logs provided tangible evidence of existing conductive faults. Drilling horizontal wells also indicated the existence of sub-seismic faults which cannot be detected by the 3D seismic resolution.Better reservoir management decisions and more focused development strategies can be achieved through the utilization of the quantitative pressure transient analysis of those tests.

One of the critical operations during the exploration phase is well testing required determining fluid type, flow rate, and the sustainability of the production. With the right planning, technology and implementation, well testing can ensure reservoir quality and production such as, permeability, initial reservoir pressure, hydraulic fracture parameters, near wellbore formation damage, geometry of the reservoir, and reserve quantities. Exploration Well Testing Operations require a complex integration of various services including surface well testing, artificial lift via coiled tubing, downhole data transmission and on-site operational activities. The increase in exploration activities involves various service companies’ proprietary data acquisition systems that introduce a challenge for decision makers due to segmented data and information. This calls for establishing an integrated unified viewer combining the operational data for engineers to enable real-time data supervision, technical support and decision making from the headquarters to well-site locations reducing operational risks and optimize required cost. This paper highlights the progress of the real time data transmission interface to support highly active exploration well testing operations in Saudi Aramco.

This paper describes case studies of observed pressure derivative signatures in the presence of stratiform Super-K permeability intervals in Ghawar field, Arab-D oil reservoir. The case studies (presented in order of increasing complexity) include:an open-hole vertical well intersecting the Super-K interval,a slant horizontal well intersecting the Super-K interval and,a horizontal well at the top of a layered reservoir, not in contact with the Super-K interval and separated from the Super-K interval by low permeability layers. The stratiform Super-K permeability intervals in Ghawar can be visualized as being like horizontal pancakes of multi-darcy permeability. Since these Super-K intervals are not continuous but rather show up as patches of high permeability, the typical effect on the pressure derivative of a vertical open-hole well is that of a radial composite system. The most complex derivative signature is observed when a horizontal well is separated from the non-intersecting Super-K interval by low permeability layers. It is very easy to misinterpret this derivative signature without integrating all the available geological and production log data. The derivative signatures are demonstrated by numerically simulated responses of actual case studies. The importance of identifying these pressure derivative signatures is illustrated in this heterogeneous, multiphase, layered, reservoir where data quality is sometimes poor due to wellbore phase redistribution. Introduction The presence of Super-K permeability intervals in the Arab-D reservoir of Ghawar field has been well documented1–7. However the effect of these Super-K intervals on pressure transient pressure derivatives has not been well described. Analysis of pressure transient test data in the Arab-D reservoir is complicated by the layering within the reservoir, presence of the Super-K intervals, multi-phase flow and wellbore phase redistribution effects. It was the objective of this study to determine what parameters are important in analyzing well tests in the presence of these unique Super-K intervals. Factors such as the impact of adjacent well production and changes in flow rate of adjacent well producers during the course of a well test have a significant impact on the pressure transients at the test well. Although equally important in other reservoirs, the impact of adjacent well interference is magnified in the presence of these Super-K intervals. Practically, analyzing slant and horizontal wells in homogenous reservoirs is complex due to the large number of variables such as Kx, Ky, Kz, Le, effective h, etc. Well tests on Ghawar horizontal wells have the added complexity of having Super-K intervals added to the mix. When these Super-K intervals are discontinuous, the complexity is increased even more. Geology The reservoir in the study area is divided into three main zones: Zone 2A at the top, Zone 2B below, which has abundance of dolomitic occurrences, while Zone 3 has the poorest rock quality. Super permeability intervals are most likely to occur in three places:at the top of Zone 2A - associated with skeletal oolitic limestone,at the top of Zone 2B - associated with leached cladocoropsis dolomite or,at the bottom of Zone 2B - associated with stormatoporoids.

An operator successfully tested an offshore, exploration well in a high-pressure and a high-temperature (HPHT) reservoir, where the pressure exceeds 10, 000 psi and the temperature is approximately 400°F. The tested intervals are behind a 4.5-inch liner. Slimhole drillstem test (DST) tools have been considered but not selected due to the restricted internal diameter and limited intervention capability. Instead, a cased hole DST method has been selected in which DST tools are set in a 7-inch liner, and tubing-conveyed perforating (TCP) guns are run in the 4.5-inch liner on the bottom of a long tailpipe. The first DST has been successfully completed, with the pressure gauges located at the gauge carriers in the 7-inch liner, several thousand feet above the test interval. Pressure and temperature data from downhole gauges have been analyzed and found to exhibit significant wellbore-phase redistribution effects because of gauge location. This has resulted in significant uncertainty in reservoir characterization. Solutions considering the HPHT and slimhole design have been investigated. We present a unique method of placing the downhole gauges on top of the perforating gun during an HPHT well test operations where formation temperature exceeded 400°F. Five DSTs have been performed using this technique with successful recording of downhole pressure and temperature data, despite the perforating gun shock and hostile environment encountered. A comparison of pressure transient interpretations as well as a comparison of data gathered by the gauges located above the guns (immediately above the perforations) with the data from gauges in the 7-inch liner will be presented to show the potential for incorrect interpretation due to the gauge placement. We will also discuss the unseen behavior of flowing gas temperature at perforation depth based on actual temperature data recorded.