Abstract

Kuwait has been drilling and producing from the deep, sour Jurassic reservoirs during the past 20 years. These vertical wells penetrate heavily fractured, highly pressured reservoirs and produce high quality light oil. There are an increasing number of wells in which depletion, low reservoir pressures and poor reservoir rock quality have meant that they can no longer flow at commercial rates. Horizontal well technology can provide a means to increase reservoir section length and intersect possible oil bearing fractures, thereby enhancing well productivity.

This paper will discuss the challenges of designing and drilling the first deep, medium radius, high pressure well bore sidetrack, from an existing production well, into the Jurassic HPHT reservoirs.

These challenges include the necessity to mill up the existing liner hanger and 80 ft. of casing to allow for any future re-completion, the restricted drill string size of 3 ½" due to the well being completed with 7 5/8" casing to surface, the directional target constraints, the hole cleaning difficulties due to the restricted pump rates, hard formations with low drilling rates, drill pipe buckling, the ability to slide in the lateral, and to drill the well without gains, losses or differential sticking.

All these difficulties were tackled using optimized drill string designs, advanced milling and directional technologies including;medium radius build profile, lateral drilling with PDC/insert bits on motors equipped with ABI (at bit inclination) for enhanced steering capabilities and LWD tools.

Using these technologies plus recommended practices developed by the operator and service companies enabled the establishment of record performances in Kuwait for this type of well.

The results of the drilling will be presented along with conclusions drawn on the overall operation which will then provide the basis for future optimization in the design and drilling of these types of wells.

Introduction

In the Umm Gudair fields there are 28 wells which penetrate the Jurassic Marrat formation.Depletion, low reservoir pressures and very poor quality reservoir rock in some wells means that they will be unable to flow at commercial rates, even after stimulation.However, there are numerous indications of natural fractures in the Marrat sub zones.Therefore, the use of horizontal well technology could provide a means to increase reservoir section length and to intersect these possible oil bearing fractures.

The present project was to re-enter one of these wells with low production potential and to drill a horizontal side-track through the most promising part of the Marrat reservoir to enhance the original well's productivity.UG-56 was chosen as the candidate well for this trial.

Background Geology

The majority of Kuwait oilfield development and related oil production is from the shallow Cretaceous formations which extend down to around 12,000 ft and which have normal pore pressures of less than 12 ppg.

From this depth the Jurassic sequence commences and this is the start of a series of highly pressured formations.

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