Horizontal Well Productivity Restoration - Successful Stimulation Application in a Large Onshore Field
Authors: Tiwari Shobhit , Singh Ranjeet , Prasad Dhruva , Kumar Pankaj , Jha Mihir , Tandon Rohit , Singh Aditya Kumar , Dangwal Gaurav 
Published: May 2016

This paper discusses the step by step procedure to identify damage mechanism and remedial treatment in horizontal wells flowing with ESP (Electrical Submersible Pump) in one of the largest onshore field Mangala situated in Barmer, Rajasthan, India. Mangala field was discovered in 2004 and was brought on production with hot water flooding in August 2009 and is currently producing at plateau rate of 150,000 bopd (barrels of oil per day). The reservoir, in general, is of high quality with multi-darcy permeability, relatively viscous (15cp) and waxy crude (wax appearance temperature only 5 deg C below reservoir temperature). The Fathegarh is the main reservoir unit which is sub-divided into FM1 (top) to FM5 (base). FM3 and FM4 are dominated by well-connected sheet flood and braided channel sands having net to gross ~80%. These massive FM3 and FM4 sands have been developed with down-dip edge water line drive water injectors and up-dip horizontal producers.

These horizontals wells (lateral length &gt;500m) are completed with screens with ICD's (Inflow Control Devices).The initial PI (productivity index) of wells has been of the order of 50–100 b/d/psi. However, with rise in water cut and increased withdrawal rate the productivity of these horizontal wells started to decline. This paper discussed the optimized production practice required to maintain optimum production rate from these horizontal wells. Due to the fact that even relatively shallow invasive near-wellbore damage may substantially impede flow; plan was prepared to identify the damage mechanism and accordingly engineer suitable remedial treatment. Envisaged damage mechanism included fines mobilization, asphaltene / wax dropouts and carbonate and sulfates scales.

An inherent problem with these wells was poor acid distribution during matrix acidizing, especially due to high permeability in long horizontal sections. The low cost systematic stimulation design and placement technique resulted into the liquid PI restoration and improved ESP performance, which has been discussed in length in the paper.

Introduction

Mangala is an onshore oil field located in northern Barmer Basin of Rajasthan state, India. The main reservoir unit is Fatehgarh which has been further subdivided into five sub units named from FM-1 to FM-5 from top to downward. Upper Fatehgarh which comprises FM-1 and FM-2, is a sinuous, meandering, fluvial channel sands whereas Lower Fatehgarh which comprises FM-3 to FM-5 is well-connected braided channel sand. Upper Fatehgarh has been developed using deviated wells with pattern as well as peripheral injectors and lower Fatehgarh has been developed primarily by drilling updip horizontal wells with downdip peripheral deviated water injectors (Figure 1). Reservoir quality of Fatehgarh sands are excellent with porosity ranging between 21–26 % and in-situ permeability between 200 md to 20 Darcy. Mangala crude oil is waxy viscous crude with in-situ oil viscosity ~ 22 cp and wax content between 18–26% and the API gravity is 28.5.

Mangala summary production performance plot is shown in Figure 2. Commercial production began in the Southern part of the field in August 2009. Mangala reached its initial approved oil production rate of 125 kbopd in 3rd quarter of 2010 and was further ramped up to 150kbopd from 2nd quarter of 2012 with higher withdrawal rate approvals. Hot water injection started in start of 2010.