–HASSI MESSAOUD Field Case Study– MESSAOUDI Khalid ⁽¹⁾, ABIDI SAAD Nouh ⁽²⁾

¹ Engineering Servicing, Technical Division, SONATRACH DP STAH, IlliZi 33000

¹ Computational Mechanics Laboratory, Tlemcen university, Tlemcen13100

² Drilling Division, SONATRACH, Hassi Messaoud, 30500

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Abstract

Nowadays, Hydraulic fracturing Techniques is the highest method that can be used to enhance oil field productivity been depleted, this technical stimulation takes different names as conventional or unconventional fracturing, but it has the same goal to allow us to increase the productivity of the injectivity in the wells. What’s the Technique that can be used? It is probably a big issue that can weaken our decision.

Due to its considering results, many petroleum companies make research planning to improve this stimulation, in particular the unconventional Technique names “Hi-Way Channel Fracturing” which was marketed in 2011 by Schlumberger. So through this study, our goal is to evaluate the results of the two Techniques after an operation of stimulation by the method of conventional fracturing and Hi-Way Techniques on the field of Hassi Messaoud. We have selected many wells having the same petrophysics characteristics and other parameters and we simulate its behavior before and after hydraulic fracturing.

Both Techniques succeeded economically. Because they are most costly, we should take all our precautions to select the candidate well for the fracturing operation.

The conventional hydraulic fracturing is an effective Technique in spite of occurrence of very advanced Techniques such as that developed by Schlumberger “HIWAY” which is very attractive, possible to significantly increase the conductivity of the reservoir permeability. The use of the fibers helps consolidate the structure of Proppants and adds high conductivity channels at the inner fracture. This technique has drawbacks that can be interpreted in a very high GOR (when the fracture reaches gas contact), so it is obvious to put into consideration precautions; in order to choose the well candidate (the problem lived in the well ONM 442).

The two Techniques have cross the near well-bore, so the two methods have the aspect of dealing with the stimulation and the increase of oil production.

With this study we will be make our decision in future which adequate Techniques to be used, we can select the performance between oil company services that make a good job. Furthermore, we can choose skillfully between conventional or non-conventional Techniques.

 I. Introduction

Hassi Messaoud field considered as one of the giant and most complex fields in the world, this important filed in Algeria is located at 850 km South-Southeast of Algiers and 350 km from the Tunisian border it covers nearly 2,200 square kilometers in area (figure 1).

The huge reservoir which has a thick sandstone was divided into many levels such as (level R3, R2, RI, Ra) Ra is the principal reservoir that has 68% of the whole. It has three productive horizons (figure 2). Now Hassi Messaoud has over than 1860 wells distributed through many areas which has different PVT parameters (figure 3).Historical overviews of hydraulic fracturing activities was presented in papers by McGowen et al.1 and by Bouazza et al.2.

The well “Om06” was been the first well undergone this stimulation Technique in 1960, between sixteen and eighteen, over than twenty five Hydraulic fracturing job was done in the field. To approve the feasibility of this Technique SONATRACH in 1990 planned a hydraulic fracking campaign spread out over three years. After this period a considerable quantity of the oil has produced from the Hassi Messaoud field originates from wells that were hydraulically fractured (figure 4).

The well “Om06” was the first well undergone. This stimulation Technique in 1960, between sixteen and eighteen, over than twenty-five Hydraulic fracturing jobs was done in the field. To approve the feasibility of this Technique, SONATRACH in 1990 planned a hydraulic fracking campaign spread out over three years. After this period, a considerable quantity of oil has been produced from Hassi Messaoud field originated from wells that were hydraulically fractured.

Until 2011 Hassi Messaoud field was known only the conventional hydraulic fracturing with classic Technique to injection mixer of water added with hard materials (sand or ceramic microspheres) for preventing the small cracks do not close once the pressure back down.

Or the Hiway technique was been introduced in 2012 and the first well that was fractured by this technic is OMN651.After that ONM442 has fractured by this technics.

  II. Hydraulic Fracturing Operation

Generally, the stimulation operation based on hydraulic fracturing require a mixer of water with other hard substance (sand or ceramic beads) to prevent small cracks to be not closing once the pressure back down. The liquid can also contain other additives to improve the viscosity of this fluid injected.

Through this technique, several objectives can be achieved, the first to create a drain in the reservoir, and other goals can be reached such as:

• Changing petrophysical rock properties
• Improving productivity or injectivity.
• Increasing the speed of recovery thanks in particular to an improvement in the productivity index.
• Increased recovery time.
• Others …

The hydraulic fracturing mechanism can be decomposed into two phases, Initiation and extension of the fracture (figure 5).

    III. Fracturing configuration

Experiments have shown that fractures are developed along planes horizontal or vertical. For depths less than 600 meters, it is possible to obtain the fractures in horizontal planes, but for depths greater than 600 meters, the weight of sediment obliges the fracture to develop only to vertical planes.

 

 

III.1. Principal stresses and fracturing orientation

At the depths exceeding to 1000 meters (where we can neglect the tensile strength versus the stresses applied to rock), theoretical orientation of the fractures will be defined by by the following relation.

III.1. Model and Propagation fracturing

Three Models of fracturing operation can be had:

III.2.1.   KGD Model

The problem is treated in two dimensions  horizontal plane (x, y), the fracture supposes that it is limited by two horizontal planes remote to height  H and constant in time, this amounts to assuming a perfect sliding along these planes (layer interface – wall rocks) and give the fracture a rectangular section in the vertical plane.

GEERSTMA Klerk (1969) (KGD) solved the problem analytically in an approximate way for a Newtonian fluid. DANESHY (1973) took into account a non-Newtonian fluid rheology. There are a relationship between height and length: XF <HF and L = 2XF (figure 7)

For this model, the calculation method is based on the following assumptions

• Single dimensional flow in direction.
• The fracture height constant on the length of direction.
• Fracture height is constant over time.
• The section of the fracture is rectangular in the vertical plane.

III.1.1. PKN Model

This model was the first that has been developed by (KERN NODGREN PERKINS) and modified by others. It can be classified as PK model, it is very useful when the stresses constraints barriers on the permeable zone are great and the pressure has increased during pumping (figure 8)

• Unconventional fracturing technique (Hi-Way)

Hi- way hydraulic fracturing technique has the same goal as the conventional technique, the first application of this technique from the company of Schlumberger was in 2010 on four new wells drilled in the Priobskoe field in Siberia. Hi-way was introduced in Hassi Messaoud field in 2012 and the well OMN651 was the first well fractured by this technique.

The principle of operation is to pump the proppant in the form of an impetus according to the design, where the blinder is programming to work with frequency steps to ensure the addition of the fiber at the same time. The fibers have some important roles during the operation, the first is to prevent the pulse dispersion, secondly the fibers ensure the opening channels inside the fracture open during pumping and closing, (figure 6) present the configuration between the two Technique.

III. Fracturing configuration

Experiments have shown that fractures are developed along planes horizontal or vertical. For depths less than 600 meters, it is possible to obtain the fractures in horizontal planes, but for depths greater than 600 meters, the weight of sediment obliges the fracture to develop only to vertical planes.

III.1. Principal stresses and fracturing orientation

At the depths exceeding to 1000 meters (where we can neglect the tensile strength versus the stresses applied to rock), theoretical orientation of the fractures will be defined by the following relation (figure 7).

III.2. Model and Propagation fracturing

Three Models of fracturing operation can be had:

III.2.1. KGD Model

The problem is treated in two dimensions horizontal plane (x, y), the fracture supposes that it is limited by two horizontal planes remote to height H and constant in time, this amount to assuming a perfect sliding along these planes (layer interface-wall rocks) and give the fracture a rectangular section in the vertical plane.

GEERSTMA Klerk (1969) (KGD) solved the problem analytically in an approximate way for a Newtonian fluid. DANESHY (1973) took into account a non-Newtonian fluid rheology. There is a relationship between height and length: XF <HF and L = 2XF (figure 8)

For this model, the calculation method is based on the following assumptions

• Single dimensional flow in direction.
• The fracture height constant on the length of direction.
• Fracture height is constant over time.
• The section of the fracture is rectangular in the vertical plane.

III.2.2. PKN Model

This model was the first that has been developed by (KERN NODGREN PERKINS) and modified by others. It can be classified as PK model, it is very useful when the stresses constraints barriers on the permeable zone are great and the pressure has increased during pumping (figure 8).

For this model the calculation method is based on the following assumptions:

• The height is constant.
• The vertical section is supposed elliptical.
• The flow in the fracture is single directional along “L”XF> HF and L = 2XF

III.2.3. Radial model

The radial pattern is characterized by a circular profile in the vertical plane with a elliptical section. It is used when the permeable zone is small. In this case a low height area is perforated, and the fracture is ensured by initial pressure at a point and expands radially. The calculation method is based on the following assumptions (figure 9):

• The height of the gap varies along the length.
• The vertical section is assumed elliptical.
• The fracture grows radially.

IV. Evaluation case study

As it is known through the stimulation operation based on Hi-way Technique or simple hydraulic fracturing operation, these Techniques can achieve many objectives, creating a permeable drain in the rock. Furthermore, other goals can be reached such as:

• Changing petrophysical properties of the rock and improving productivity or injectivity.
• Increase the time and the speed of recovery
• Improve the productivity index.
• Decrease the differential pressure at the edge of the well bore to remove paraffin deposition problem and asphaltene.

IV.1. Steps to select the wells for evaluating study

For a best evaluation study many steps has been fixed to select the wells that can guide us to the reliable results, so the steps are:

• Select the wells fractured by Hi-WAY Technique
• Select the wells fractured by conventional Technique in the same period
• Select the drains for the two Techniques
• Select the levels of Hiway fracturing (D5, D3, ID)
• Select the wells fractured by conventional Technique at the same level
• Select the wells which have the reservoir pressure
• Select the wells which have the same quantity of proppant
• Select the wells which have the same petrophysics parameters Porosity ø, Permeability K

The steps and the position of the wells fractured with Hiway technique in Hassi Messaoud Field are shown in the (Figure 10) and (figure 11)

IV.2. Fracture job evaluation

OMN651 and ONM442 were fractured by Hiway technique, these wells selected with other wells fractured by conventional techniques like MD 530, MD257, MD30 and MD133, will guide us to remove the ambiguity that may happen when taking decision to realize the fracturing job for each well.

IV.2.1. Valorization of the results between OMN 651, MD257, MD530

IV.2.1.1. WELL OMN651

ONM 651 was drilled in January 2010, completed with tubing Production 4 “1/2 New Vam, its DST has given 56,52 bbl/h with a drawdown of 753.83psi and a skin=-5. The well was acidified 21/03/2011. The interpretation of last BUP (30/05/2011) after acidification shows a drawdown of 2645.54 psi and a skin 0.1 that means that there is a problem between the reservoir and the near wellbore. [4]

The results obtained before fracturing job in May 2012 gave an oil flow rate = 4,77 bbl/h and GOR = 161 for Pt = 388.29 psi and Choke= 0,47in.

The introduction of a new technology to the field, OMN651 selected the first well undergo this new technique, thermometer measurement shows that the fracture is developed on the 11220.44ft to 11482.9 ft, corresponding drains D5, D3, D2 and the top ID

The results of the fracture are shown in the figures 12, 13 and the table 1 and table 2.

Table 1: Fracturing Geometry OMN 651[4]

Fracturing technique	HI-WAY
Xf (Length)[m]	106.8
Yf (Height) [m]	85.5
Ef (thickness) [in]	0.054
Pressure [Psi]	2403

Table 2: Shows the results of stimulation job by Hi-way technique [4]

	Design (Simlated)	2nd Re-Design	Execution
Linear Fluid vol & type	WF135-7,845	WF135-7,930	WF135-8,148	gal
Cross-Linked Fluid Vol & type	YF135HDT-55,197	YF135HDT-60,337	YF135HDT-53,852	gal
Total Slurry Volume	1562.0	1523.1	1543.5	bbl
Type Of Proppant	20/40 HSP	20/40 HSP	20/40 HSP	–
Total proppant	77441	79122	85434	lbs
Total Proppant In formation	77441	77442	82939	Lbs
PAD % (dirty)	34.5	32.1	31.8	%
Rate	20	20	20	bbl/min
Last BH Prop Concentration	8.0	8.0	8.0	PPA
ISIP Surface / BH	7184/12038	6822/11748	4706/9698	Psi
Average surface Pressure	6202	4399	4942	Psi
Maximum Surface Pressure	7669	7342	5614	Psi
Net Pressure	1288	4405	2403	Psi
Efficiency	32.1	36.5	28.7	%
Propped half length	26.6	77.1	106.8	m
Propped height at wellbore	82.3	85.5	91.5	m
Average Propped width	0.359	0.148	0.054	in
Effective Fcd	212.4	97.5	97.5
Leak off coefficient	7.0E-3	2.4E-3	2.1E-3	Ft/min
Spurt	2.0	0.2	0.2	gal/100Ft

 

By nodal analysis before and after job fracturing (figure 14) the results showed a negative Skin= –5.61 and potential of 49.42bbl/h, the technique of fracturing Hi-way proved its efficiency to stimulate the well.

However, to clarify this efficiency, the accumulates of 4 months of oil produced after fracturing Hi-way job has been calculated and the result of this later is shown in (figure 15)

IV.2.1.2. WELL MD257

The well was drilled and completed in October 1970 with 5”x4”1/2, this well is located in the zone 1B, its DST April 1976 has given 53,38 bbl/h  [22],it build up (February 2009) gave an oil flow rate= 22.23bbl/h

Many operations of snubbing and coiled tubing were done for cleaning its well bore. The Latest result before fracturing job (April 2010) gave an oil flow rate of 0,8 bbl/h ,GOR= 244 , Pt=197.70 psi and Choke= 0,47mm.

The Shadow frac has been done in October 2010, thermometer measurement shows that the fracture is developed from 11220, 47ft to the unknown trajectory, but the goal was the bottom of D5 and the top of D4.

The results of the fracture are shown in the figures 16, 17 and the tables 3,4,5.

Table 3: Fracturing Geometry MD257

Fracture half-length [m]	27	Fracture half length [m]	27
Total height [m]	41	Total height of proppant [m]	41
Upper side of the fracture [m]	3416	Upper side of the fracture [m]	3416
Lower side of the fracture[m]	3457	Lower side of the fracture [m]	3457
Fracture efficiency of the slurry	0.17	Maximum thickness of the fracture [in]	0.78
Average concentration of the proppant [lb/ft2]	5.34	Average thickness of the fracture[in]	0.52

Table 4: Fracturing conductivity MD257

Average conductivity [md.ft]	4862.4	Average thickness Frac  [in]	0.51
In-Dimensional conductivity	3.62	Permeability of formation [mD]	15.3
Damage factor of proppant	0.50	Undamaged prop perm at stress [mD]	323666
Total factor damage	0.50	Permeability of proppant with proppant damage [mD]	161833
effective length of proppant [m]	27	Permeability of proppant with damage [in]	161833

 Table 5: Hydraulic fracturing pressure MD257

Net pressure model [Psi]	1733	BH stress closing of the frac	8414
Recorded pressure [Psi]	2436	Gradient of stress closing [Psi/ft]	0.747
Well head pressure [Psi]	5912	Average pressure (surface) [Psi]	3226
Reservoir pressure [Psi]	4857	Max Pressure (Surface) [Psi]	8394

 

The nodal analysis base on DST before and after (figure 18) shows that the technique conventional has taken its positive results negative –6.96 Skin and potential of 11.48bbl/h, GOR=538, Pt= 1024.08 psi and Choke=0,47in, Furthermore the fracturing had passed the damage zone (near well bore).

With the same way of OMN651 result, MD257 can be shown after calculating the accumulates of oil production during 4 months. the quantity of the oil produced is shown in (Figure 19).

 

IV.2.1.3.        WELL MD 530

MD530 was drilled in February 2001 and completed with tubing 4”^1/2 NV,the reservoir and the well were recovred with LCP, scrapping operation and bull heading by treated water 2-3 times per month were done.

Its potential has decreased progressively from 4bbl to 0.5bbl/h, the well has been undergone many clean out operations; in order to restore its potential, but the result was nagtive.

The quantitative interpretation of PS-GHOST realized in 22/07/2002 showed that about 65.48% of the production of gas with 57.82% of oil comes from perforations located between 11181,10 ft  and 11302,49 ft which corresponding to the middle of  D5.

Contrariwise 34.52% of gas and 42.18% of oil come from the series of perforations located between and 11323,81 ft and11333,66 ft, 11320,53 ft and 11307,41ft, as well as 11302,49 ft and 10958ft m located in the lower part of D4.

One cleaning operation with reformat was done in 26/12/2008, but without positive result.

20/03/2009: Clean Out, TD = 11633,85ft

28/04/2009: Cleaning with Coiled Tubing, TD = 11633,85 ft

26/06/2009: acidification operation, the flow rate increased from 0.4 bbl/h to 1.39 bbl/h. The Shadow frac has been done July 7, 2010, the thermometer log showed that the fracture is propagated between 11161,41 ft m to 11423,8 ft corresponding to the drains D4, D3 and D2 TOP. The result of the fracture is shown in the figures 20, 21 and the table 6.

Table 6: Result of frac design MD530 [4]

	Design (Simlated)	2nd Re-Design	Execution
Linear Fluid vol & type	WF135-7907	WF135-7810	WF135-8465	gal
Cross-Linked Fluid Vol & type	YF135HDT-47900	YF135HDT-41300	YF135HDT-42546	gal
Total Slurry Volume	58548	51849	52966	bbl
Type Of Proppant	20/40 HSP	20/40 HSP	20/40 HSP	–
Total proppant	80000	80000	82104	lbs
Total Proppant In formation	78020	78020	81402	Lbs
PAD % (dirty)	59.2	56.8	56.2	%
Rate	40	40	40	bbl/min
Last BH Prop Concentration	8	8	8	PPA
ISIP Surface / BH	6820	5220	5486	Psi
Average surface Pressure	7100	6500	6817	Psi
Maximum Surface Pressure	8337	6994	7644	Psi
Net Pressure	1910	1608	1823	Psi
Efficiency	16	18	12	%
Propped half length	66.1	64.1	64.8	m
Propped height at wellbore	35.9	44.9	38.1	m
Average Propped width	0.129	0.137	0.141	in
Effective Fcd	294.4	>400 (Permeability is unknown)	>400 (Permeability is unknown)	–
Leak off coefficient	9E-3	8E-3	1.1E-3	Ft/min
Spurt	2	2	2	gal/100Ft

 

The nodal analysis before and after (figure 22) shows that the technique conventional has taken its positive results, negative Skin = –6.59 with potential of 3.55bbl/h. Pt=95,9Kg/cm2 and Choke=12 0,47, Furthermore the fracturing had passed the damage zone (near well bore).

MD530 after calculating its accumulates of oil production during 4 months, the quantity of the oil produced is shown in (Figure 23).

Table 7: Results were obtained before and after job fracturing

Well name	Results before Frac		Results after Frac		Frac Results		Q(m3/J)
	Qbef (m3/h)	Skin Befor	QAft (m3/h)	Skin After	QF(m3/h)	Skin F
ONM 651	4,77	-3,03	7,87	-5,61	9,26	-5,96	81,95
MD 530	0,98	7,14	3,55	-6,58	2,4	-5,96	39,97
MD 257	0,89	13	11,46	-6,96	4,07	-4,89	181,41

  V. Economic Calculation

For each well we have chosen four months such as production period, the target is to assess the performance of each technique during this period, and extract the efficiency of this versus the results were having from the conventional techniques in Hassi Messaoud field.

The first observation that can be extracted when the conventional technique used in the wells 257 MD gives us a gain 22133m3, which is benefit to the company if we compere this results with OMN651(fractured by the Hi-Way) potential production, OMN651 shares the same filtering criteria with the MD257 and MD530 well.

To know the profitability of these hydraulic fracturing operations, a calculation of payback time is realized by the following classic formula:

G: Gain of oil production after frac [$/Jour]

P: price of barrel oil price

The results obtained have shown in the table 8:

Table 8: Gains and amortization time for each well

Well name	GAIN (m3)	GAIN (m3/J)	Price ($/J)	job cost ($)	amortization time (Days)
ONM 651	9998	81,95082	20618,826	690080	33
MD 257	22133	184,44167	46405,523	6117219	13
MD 530	4877	39,97541	10057,813	754314	75

 

In (Figure 24) is the amortization of each wells according to the number production days shows a clearly that the gain of conventional fracturing technique (MD530 and MD257)  is very important while compare it with the gain that have been extracted after the stimulation job from ONM651 well.

VI. Conclusion

This evaluation study allowed us to extract some very essential points:

Conventional fracturing technique is an effective technique in spite of the appearance of highly advanced techniques such as developed by Schlumberger “HIWAY” it was very attractive to increase significantly the conductivity of the reservoir (permeability). The use of fibers allows the structure of Proppants to be consolidated and create a drain with high conductivity the inner fracturing. This technique has drawbacks that can result in very high GOR (when fracture reaches the gas contact), so it is obvious to take all our precautions to choose the candidate well (the problem OMN442 lived in the well).

Both techniques have succeeded to pass the damage zone (near well-bore), so the both techniques can treat, stimulate and increase the production of oil. Thus these Both techniques can eliminate or reduce the interventions on Wells (Coild Tubing, Sunnbing …)

For economic aspect, the two techniques are very expensive and especially the HiWay techniques, so the right choice of candidate wells allows us to reduce costs while we increasing the oil production and reduced GOR (avoid comes gas or water).

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