Drilling and Well Completion Problems in Geopressured Formations of the Carpathian Basin
Authors: Alliquander Odon , Csaba Josef 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the SPE-European Spring Meeting 1976 of the Society of Petroleum Engineers of AIME, held in Amsterdam, The Netherlands, April 8–9, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal, provided agreement to give proper credit is made.

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Exploration drilling in the Carpathian Basin is extremely risky in view of the presence of overpressured formations. This can presence of overpressured formations. This can easily cause blowouts. The simultaneous use of drilling rate and modified "d" factor logs combined with a calculated log of the drillability factor has proved to be a suitable method for detecting relatively thin, overpressured transition formations. A complementary method exists in observing change in flowline mud temperature.

Bringing the deeper, heavily overpressured reservoirs into production is also a most difficult job. Perforating the casing at a depth of 4,000 m will easily result in a rapid production decline because of the early closing production decline because of the early closing of the overpressured reservoirs and because rock debris fills the well. Acid fracturing and opening only the most permeable intervals seems to be the best method of maintaining well productivity. productivity

Introduction

The statement that use of balanced drilling technology and avoidance of blowouts are key problems for economically drilling deep and very problems for economically drilling deep and very deep wells is considered valid on a world-wide basis. Doing this in the Carpathian Basin is difficult. This is because some Pliocene formations constitute a thick sequence of rock layers and some lower-Pannonian sandy formations, as well as Pliocene-Miocene base conglomerates and Miocene or older formations lying below them are largely overpressured; and partly because the geothermic gradient there is partly because the geothermic gradient there is of abnormally high value. Fighting against potential kicks-threatening blowouts—is also potential kicks-threatening blowouts—is also difficult because, over the points where kicks occur, the Pannonian formations are in a relaxed state. They tend to be fissured nearly vertically and the fissures starting from the borehole may reach the surface even when formed at great depth.

For designing the structure of boreholes, therefore, it is very important to locate initially any overpressured formation at least on a correlation basis, or at a new site, drilling wild-cat holes, by evaluating adequately the obtained seismic data, respectively.