Abstract

Field test results of a 12-1/4 " fluid hammer tool are presented. This field test was conducted in the shallow section of the intermediate hole (4500') through the Barranqu?n Formation, which is the hardest and abrasive section within the Alochtonous Cretaceous Block, Eastern Venezuela. Test's principal objectives were to understand tool's performance under specific and controlled drilling parameters.

This trial is the second one conducted in the same formation. It was planned and operated in order to reduce the associated risk of testing new drilling technologies. Careful attention was given to choose a well section and operations schema that assured a maximum control over the field test.

Test results and field observation show a strong relationship between hammer, drillstring and drilling parameters on tool's performance. The driller operated the hammer with conventional drilling equipments and procedures. He drilled with low Weight on Bit (WOB), and low rotational speeds (RPM). Flow rates increased accordingly to keep Stand Pipe Pressures (SPP) and differential pressure through the hammer constant. However, keeping them as planned was difficult. The test lasted 5 hours in which the equipment drilled 20 ft for an overall rate of penetration (ROP) about 4 ft/hr. Instantaneous ROP were higher than offset wells (5.5 ft/hr) but a better understanding of the whole system must be carried out in order to further develop an entire system that can sustain a constant and high ROP.

Introduction

The Alochtonous Cretaceous Block is a complex geological structure (8000 - 12000 feet thickness) located in the Northern Monagas fields, Eastern Venezuela. It is characterized by several heterogeneous and abrasive formations. These formations are currently drilled with a 12-1/4 " bit for the intermediate hole, which represents more than 50% of the drilling well costs in the area. Drilling performance through this section has been affected by low rates of penetration and frequent unplanned trips caused mainly by bits wear and tools failures.

Several bit technologies have been used on previous offset wells to overcome drillability problems. However, tricone bits still remain as the ones whose price/performance ratio has been favored. Mainly, because their versatility in interbedded lithologies such as those placed in the Barranqu?n formation. On the other hand, ROP improvements seem hard to reach and sustain with current bits technology for such a formation. Nonetheless, developing, understanding and evaluating new drilling technologies are key factor for future developments in the Northern Monagas fields. This led PDVSA to consider Percussion Drilling through the use of Fluid Percussion Hammers, as a potential technology capable of overcoming the challenge of reducing drilling costs in hard rock/ hard to drill formations.

The first test with a Fluid Hammer tool in PDVSA was during 1999 in a Northern Monagas(1) exploratory well. Depth ranged from 14293 ft to 14302 ft through the Barranqu?n Formation. After two attempts in this well, ROP was about 1.4 ft/hr, far below previous offset wells (5.5 ft/h). Some periods of high instantaneous ROP were noticed. Several uncontrolled variables affected tool's performance at that depth.

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