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Advances in Ma terials Physics and Che mist ry, 2012, 2, 193-196
doi:10.4236/ampc.2012.24B050 Published Online December 2012 (htt p://www.SciRP.org/journal/ampc)
Copyright © 2012 SciRes. AMPC
Research of Extent of Well Control of Explored Reserves of
Lithologic Deposit in Delta Front Area
NO. 9 Oil Production Company, Daqing Oilfield Company Ltd. Daqing, China
Recentl y the explored reserves submitted in the oil field mainly situate at the end of deposit in delta front area. During the exploita-
tion and production, problems mainly show on lithologic deposit, for example, reserves are low and difficulty of producing is huge .
Based on results of sand body dissection of dense well network of developed oil deposit, and combined with explored reserves, this
article researches a relation between extent of well control and reserves precision of explored reserves of lithologic deposit in delta
front area by well diluted method. This article has significant influence on objectively understanding our une xploite d re s e rves.
Keywords: Delta Front; Lithologic Deposit; Extent of Well Control; Well Diluted Method
Till the end of 2008, the amount of our explored but unex-
ploited geologic reserves are 2.5122×108 tons, including
70.22% unexploited reserves in Putaohua layer of main layer.
This part of reserves are mainly distributed in delta front area
where is far away from source, sand body is scattered, and the
main type o f reservoir s is small-si zed lithologic deposit.
Submission of explored reserves should satisfy the require-
ment that completed wells satisfy development plan and can
control productive limit or l-aqueou s interface. There should be
a reasonable exten t of well co ntrol: rel atively high extent caus-
es invention waste and delay of exploration of lithologic depo-
sit; relatively low extent cannot control change of lithologic
deposit. Currently, the submitted explored reserves are gener-
ally with low extent of well control and hard to effectively con-
trol highly hidden lithologic deposit with scattered sand body.
Besides, affected by seismic resolution, reservoir forecasting
techniques cannot efficiently recognize thin interbeded reser-
voir, causing l ow developing degree o f reserves.
This article bases on results of sand body dissection of dense
well network of Longhupao oil field, Longnan oil field, Putao-
hua oil field and Gaoxi oil field, applies well diluted method,
and researches a relation between extent of well control and
reserves precision of explored reserves of lithologic deposit in
delta fro nt area.
2. Research of Extent of Well Control of Litho-
2.1. Characteristics and Types of Lithologic Deposit
Putaoh ua layer is mainl y located i n del ta front area; t he prop or-
tion of its sand ground is moderate; it is oily in wide area, and
the type of oil reservoir is mainly lithologic deposit. According
to the planform of sand body of reservoir storage, lithologic
deposit can be separate into three types: lenticular sand reser-
voir, banded s and reservoi r , and sheet sand reservoir.
Lenticular sand reservoir is mainly located in abandoned
channel, mouth bar, and distal bar developing. Sand body is
surrounded by non-permeable mudstone; it has independent
oil-water systems; oil area is small; the plane distributes sepa-
rately; sand drilling rate is low, about 30%. Statistics of the
accurate dissection of dense well of oil field indicates that the
width of lenticular sand body ranges from 100 to 300 meters,
and evaluation well is uneas y to be controlled.
Banded sand body reservoir is mainly distributed in channel
sand developing area. Space among channels is filled with
thin-bed sand sheet or mudstone; aeolotropism of plane is high;
strike direction of sand body extends far, and sideway is narrow.
Sand drilling rate of sandstone generally ranges from 30% to
40%. Statistics of the accurate dissection of dense well of oil
field indicates that the width of banded sand body is between
100 and 350 meters.
Sheet sand reservoir is mainly distributed in sand sheet de-
veloping area. The area is large, thickness keeps steady, and
Sand drilling rate of sandstone is usually over 60%. Statistics of
the accurate dissection of dense well of oil field indicates that
the width of sheet sand body is between 300 and 600 meters,
which means evaluation well is easy to be controlled.
2.2. Analysis of Current Situation of Extent of Well
Control of Developed Lithologic Deposit
The oil field was producing explored reserves of lithologic
deposit of Putaohua layer in delta front area, due to low extent
of well control, we suffered some problems, for example, pro-
ducing degree of reserves is low and adjustment of deliverabil-
ity construction is frequent.
Gaoxi oil field finished drilling 22 evaluation wells in 1983,
and submitted 1100.00×104t of triple IOIP, in which the oil
area is 53.0km2, and the extent of well control is 0.42 well per
km2. In 1994, we designed 104 drilling wells, in which 8 were
finished drilling. After drilling first well and research again, we
revised p lan: planned well sites were 73 and 31 were canceled.
Copyright © 2012 SciRes. AM PC
During the exploitation of drilling wells, according to under-
standing of rolling drilling geology, we canceled 23 planned
wells. In 2002, we recalculated reserves: oil area is 26.8km2,
finished drilling wells are 25, and the extent of well control is
1.12 well per km2. From the history of adjustment, reserves
changes with the change th e ext ent of well co ntro l.
22 wells in Gulong oil field Gu 571 block were finished
drilling in 2007. In explored reserves, the amount of oil area is
46.7km2, and the extent of well control is 0.47 well per km2.
After finishing drilling 97 wells, according to principle of con-
touring of productive limit of explored reserves, preliminary oil
area was cut into 29.8km2, and the extent of well control was
raised to 2.5 wells per km2. One well in Gao 20 district was
finished drilling in 2007, in which the oil area is 4.5km2, and
the extent of well control is 0.22 well per km2. 8 wells were
rolling drilling in 2009, footage is 14855 meters, and the extent
of well control was raised to 2 wells per km2. Preliminary the
amount of oil area was 1.38km2, explored reserves 41.85×104t,
and average reserves is 0.0028×104t per meter of footage. Be-
cause of the low extent of producing reserves, the risk of ex-
ploitation is huge.
2.3. Relation betw een Extent of Well Control and
Reserves Precision of Explored Reserves
Reason able extent o f well contr ol is a key to exp lore reser voirs
and to effectively exploit. Especially, using the location of
evaluation wells to evaluate lithologic deposit in reservoir bed
with multivariant lithologic characters can hard to understand
rules of geology, thus bringing big exploitation risks. On the
contrary, to small-sized lithologic deposit, unreasonable extent
of well contro l often causes excess of dr illing wells.
Calculation formula of IOIP by volumetric method:
Parameters description: N,IOIP, 104t; Ao,Oil Area, km2; h,
Effective Thickness, m; Φ, Active Porosity, <0; SWi, Initial
water saturation; ρo, the density of STO, t/m3; Boi, Oil Volume
Factor , m3/m3;
According to parameters in formula, the extent of well con-
trol has different influence extent on different sandstone stypes
of lithologic deposit.
To lensing reservoir, because the area is small, influence on
reserves b y extent o f well control is mainl y variatio n of oil area
(Ao); to banded sand body reservoir, due to its banded distribu-
tion, influence on reserves by extent of well control is mainly
variatio n of oil area (Ao) either; And to sill-like reservoir , since
its reservoirs are well continued and area is big, influence on
reserves by extent of well control is mainly variation of Effec-
tive Thicknes s ( h).
In order to study the relation between extent of well control
and reserves precision of explored reserves of lithologic deposit,
we start at results of the accurate dissection of dense well of
sand body of Longhupao oil field, Gaoxi oil field, Longnan oil
field, and Puxi oil field, and expand our research by using well
diluted method. This article, starting at extent of well control 16
wells per km2, made statistics of proportions of omission of
sandstone under different extent of well control. (Figure 1).
According to Figure 1, when extent of well control reaches
6.25 wells per km2, the proportion of omission of sandstone is
about 50%. Therefore, to control sand body above 50%, the
extent of well control cannot be below 6.25 wells per km2.
In order to explain that different extent of well control has
different influence on reserves precision, we selected 4 oil
fields with 49 typical lithologic deposits in different types, and
finally made statistics and regression of errors in explored reserves
under diffe rent extent of well control. (Shown in chart 1).
Errors in reserves of three types of lithologic deposits be-
come larger with decreases in extent of well control. Besides,
extent of well control affects reserves precision of sill-like re-
servoir less than affects that of lensing reservoir and banded
In light of the different requirements to errors in explored
reserves with various levels, we can summarize extent of well
control of explored reserves with different kinds of reservoirs.
Oi l Fi e ld Number of Sandstone
Ext ent of Well Control
16 wells/k m2 11.1 wells/km2 6.25 wells/km2 4 wells/km2 1.56 wells/km2 1 we l l/km2
Gaoxi 92 26 28.3 33 35.9 44 47.8 73 79.3 84 91.3 85 92.4
Puxi 260 52 20.0 83 31.9 104 40 175 67.3 185 71.2 227 87.3
Longnan 419 116 27.7 136 32.5 249 59.4 261 62.3 370 88.3 373 89.0
Longhupao 271 26 9.6 52 19.2 82 32.9 172 63.5 219 80.8 236 87.1
Figure 1. Statisti cs of omission of sandstone under different extent of well contro l in delta front area.
Copyright © 2012 SciRes. AM PC
Chart 1. Relation between reserves prec ision and diffe ren t ex t ent of well contro l.
Explored R eserves Pro d uc ed
（Type I） Explored Reserves Unproduced
（Type II） Basic Explor ed Reserves
（Type II I）
Lenticular sand body reservoirs ＞16 11.1～16 8.2～11.1
Banded san d body re se r v o irs ＞11.1 8.2～11.1 6.25～8.2
Sheet sand body reservoirs ＞6.25 2.8～6.25 1.8～2.8
Relative Error (%) 10 20 30
Worthy to mention that the winding of rivers causes diversi-
fication and irregularity of lithologic deposits, especially
banded reservoir. This evaluation of reservoirs is not fully ap-
plicable to conventional standard well network. Thus, people
should flexibly design pattern configuration in different types
of reservoirs by utilizing research findings of extent of well
control. It has been found that it is better to use well network
with regular dimensions in sill-like reservoir but to use “S”
pattern in banded reservoir----well spacing can expands along
with strike direction of sand body while horizontal distance is
better to be limited within the width of wave of sand body, not
only accelerating evaluation but also well controlling oil area
and improving evaluation precision.
3. Conclusions & Suggestions
First, in delta front area, the width of lenticular sand body re-
servoir ranges from 100 meters to 300 meters, banded sand
body reservoir from 150m to 350m, and sheet sand body reser-
voir from 300m to 600m.
Second, producing degree of explored reserves of lithologic
deposits in delta front area mainly depends on extent of well
control. In order to control sand body above 50%, the extent of
well control cannot be below 6.25 wells per km2.
Third, according to different requirements to reserves preci-
sion with different level, lower limit of extent of well control o f
explored reserves of lensing reservoir, banded reservoir and
sill-like reservoir is 8.2 well per km2, 6.25 wells per km2, and
1.8 wells per km2 respect ively.
In exploitation and production of explored reserves in delta
front area, we should firstly develop well，enhance extent of
well control and strengthen geology knowledge, and then de-
velop exploitation wells and decrease drilling risks.
 Shen Showwen, Peng dajun, et al，Clas sification And Explora-
Copyright © 2012 SciRes. AM PC
tion Methods Of Subtle Trap Reservoirs, ACTA 2000, 21 (1):
 Huang Wenying. Research on the relation between well control
degree and proven reserves of Shengli Oilfield. PGRE,