Evaluation of Formation Damage and Fluid Loss Control Potential of Formulated Water Based Mud with Corn Cob Particles

Evaluation of Formation Damage and Fluid Loss Control Potential of Formulated Water Based Mud with Corn Cob Particles

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Godwin Chukwuma Jacob Nmegbu, Emenike N. Wami, and Bekee Bari-Agara

Department of Petroleum Engineering, Rivers State University, Nigeria,

Abstract The formation damage and fluid loss control potential of water based mud formulated with corn cob particles treated with sodium hydroxide as a partial replacement for polyanionic cellulose (PAC) has been studied. Core samples were obtained from a well in Nembe Creek in the Niger Delta at a depth of 5400 feet and stored in a humidity-oven. The core samples were invaded with the formulated mud using a liquid permeameter to force the mud through the core sample at certain pressure. Physio-chemical properties such as moisture content, ash content, volatile matter, hemicellulose and cellulose were analysed and results obtained showed that cellulose content increased in the cob when treated with sodium hydroxide solution. Porosity of core samples was between 16.65- 22% and permeability was up to 5,890mD. Fluid loss volume over time was highest at 12.61mls in mud sample with only corn cob particles as the fluid loss additive and was within6.5- 10.49mls in samples with different percentage combination of corn cob and PAC particles. Rheological properties such as apparent viscosity, plastic viscosity, yield point and gel strength decreased as the percentage concentration of corn cob increased in the mud samples. These properties decreased gradually as temperature increased from 80OF to 200OF. Mud samples with 25%-75% and 50%-50% corn cob to PAC particles showed good rheological properties close to those of the standard mud. pH was slightly higher at 10.2 in mud sample with 100% of corn cob particles as fluid loss additive but lower at between 7.5-7.8 in samples where corn cobs were combined with PAC. Differences in initial and final permeability of the core samples were used to calculate the percentage damage on the core. The mud sample containing 100% corn cob as fluid loss additive caused more damage of 42.3% at 50 psi and 62% at 100 psi respectively but percentagedamage reduced in samples containing different combinations of PAC and corn cob particles.

Keywords Corn cob, fluid loss, rheological properties, formation damage, percentage combination

I. INTRODUCTION

Drilling operations expose the producing formation to the drilling fluid and any solids and chemicals contained in that fluid. Some invasion of fluid filtrate and / or fine solids into the formation is inevitable. Damage to the formation can occur either near the wellbore face or deep into the rock during several processes such as drilling, coring, well completion, production, work over by physically plugging of pores by mud solids, rock wettability alteration, insoluble material precipitation in pore spaces, migration of fines into pore throats, introduction of an immobile phase and formation of an emulsion and blockage. On average, the cost

of drilling fluid is 15%-18% of total well cost [1]. However, a small marginal spend on drilling fluid can be offset by a superior fluid performance achieved which translates to cost savings and lowers total well cost.

A drilling department can be adjudged to be successful when the well is drilled and cemented at a reduced cost without major problems. However, upon handing over to the production department, any fluids or solids invasion will affect production adversely and the same well could be seen as a failure.

A good number of wells are completed without casing and perforations and in these completions, near wellbore damage is not by passed by perforations. Hence formation damage has to be minimized because avoiding it is not possible. The type of drilling fluid used is one of the most important factor that determine the success of a well drilling operation, the ability to minimize formation damage or seal permeable formation by reducing fluid passage into the formation. The drilling operations are however faced with lots of challenges and among them is the drilling fluid loss. Fluid loss which results in formation damage can be minimized using a wide range of additives in the drilling mud [2,3,4,5,6,7, 8]. The use of local materials is also advantageous in terms of cost [9, 10, 11]. Huge amount of money spent yearly by the industry to combat fluid loss and its after effect which in some cases leads to abandonment of expensive wells. Estimates put cost of fluid losses in the industry around $800 million yearly, and fluid loss products cost around $200 million [12]. To combat this several cellulose based additives have been proposed but are expensive therefore the need to test other raw materials that can serve the same purpose become necessary. This work will evaluate the potential of formulated water based mud with corn cob particles to control fluid loss and formation damage.

II. MATERIALS AND METHODS

A. Equipment and InstrumentsB. Reagents/Chemicals and other MaterialsC. Experimental ProcedurePhysiochemical Properties TestMud FormulationPetrophysical Properties TestPercentage Formation DamageA. Physio-Chemical Properties of Raw MaterialTable 2: Physio-Chemical Properties of Raw Material (Corn Cob) Before and After Alkaline Treatment with Sodium HydroxideB. Fluid Loss in Formulated Water Based Mud SamplesC. Formation Damage by different mud samplesD. Permeability of Drilling Mud Invasion at 50 psi Injection PressureE. Permeability of Drilling Mud Invasion at 100 psi Injection PressureF. Plastic Viscosities of Mud Samples at Different TemperaturesG. Apparent Viscosity of Mud Samples at Different TemperaturesH. Yield Point of Mud Samples at Different TemperaturesI. Gel Strength in Formulated Mud Samples at Different Temperatures

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