Underbalanced Production Steering Delivers Record Productivity
Authors: Pia Giancarlo , Fuller Tom , Haselton Thomas , Kirvelis Ringys 
Published: December 2007

The independent JV Operator UAB Minijos Nafta has interests in six onshore fields in the Gargdzai Region of Western Lithuania. Past experiences in this region using conventional overbalanced drilling techniques showed that the Middle Cambrian Sandstone reservoir, with its very low porosity and permeability, is highly susceptible to invasion damage with resultant high skin factors and poor productivity. Some 8 – 10 wells were drilled in the period 1966 – 1996 with uniformly disappointing results and production rates ranging at best to only to 130 bopd. Total license production in 1995 was in the region of only 400 bopd.

In 2000 the operator embarked upon a new drilling campaign with the intent of using underbalanced drilling methods in an attempt to eliminate formation damage, test whilst drilling and drill & complete future wells in underbalanced conditions.

One of the most significant factors contributing to the continuing and accelerating success of this campaign is the initiation and continuing improvement of a technique we have named "Underbalanced Production Steering".

The basis of this technique was simple: the ability to steer the well using the directional BHA in response to the production whilst drilling as measured on the separation system.

The technique required no high technology MWD/LWD, simply a standard underbalanced drilling surface system yet delivered extremely high productivity by optimising placement of the wellbore within the reservoir. This paper will look at the history of the area, and in more detail at the Production Steering Technique.

Beginning with Pietu Siupariai #2 (PS – 2), six wells have been drilled to date with the techniques and safety measures being refined throughout the campaign by constant consultation between the Operator and Weatherford UBS, the underbalanced drilling contractor. Each well from PS – 2 through PS–4 showed encouraging results, with initial production rates up to 30 times greater than those achieved with conventional overbalanced drilling. After PS-4, the next well, Anseniai-1, was drilled in a unique fashion with duel legs, the first drilled overbalanced with a DST which indicated minimal production. This leg was plugged back then oriented roughly 180 deg and drilled horizontally underbalanced to TD, delivering excellent productivity. The following well Diegliai-8 was also drilled horizontally and has delivered the record well productivity in Lithuanian Oilfield history. The following well, Pociai-6 has also delivered outstanding productivity, this well featuring a dual open hole lateral within the reservoir section, both being drilled using the "Production Steering" technique.

In all cases, the "Production Steering" techniques has been gradually refined from the initial simple directional well in PS-3, followed by the first horizontal well: PS-4, to the first "Production Steering" well: AS-1H, D-8 and the first "Production Steered" dual open hole lateral well:P-6.

In addition, the oil produced while drilling contributed positively to the overall economics of the program – two of the three Pietu Siuaeriai wells were paid for within 4-6 weeks of completion whilst D-8 was paid for by TD with the production obtained during drilling.

This paper will briefly review the drilling and Production history of the region and detail the underbalanced drilling program that evolved from close cooperation with the Operator. It will describe in detail the concept of "Production Steering", the use of MWD data together with fluid influx data to steer the well into the higher productivity layers of the reservoir, and highlight the innovative relationships established during the drilling program. Finally it will discuss the ongoing drilling program that has evolved and the latest results achieved.